rarely capable of encroaching. But there are limits to this resistance of the waves, which, with some related phenomena of coast-action, we must proceed to consider. Professor Phillips, in his 'Memoirs' of his uncle, Dr. William Smith [PHILLIPS, JOHN, and SMITH, WILLIAM, in BIOG. Div.], has sketched in the following comprehensive manner, the philosophy of the Norfolk sand dunes, and their relation to the changes of the coast-line.

Along all this coast (from near Happisburgh to Winterton) the sea might enter, and spread in broad and winding sheets over 40,000 acres of land, but for a natural barrier of sand-hills, thrown up into a narrow irregular ridge by the action of the sea and the wind, and fixed by the growth of the 'marram,' or Arundo arenaria. The set of tide along this coast is from the N.W., and this being the line of the mud-cliffs and sand-hills, the whole of the sea-barrier thus described is raked by the currents, and the materials of which it is composed are perpetually drifted to the S.E., to augment the mass of sand-banks about Yarmouth Haven. The wasting of the cliffs to the north supplies the materials for the aggregation and renewal of the sand-hills, or dunes, and the whole coast is in motion; so long, however, as the sand-hills maintain a continuous unbroken line, they offer an effectual though variable barrier to the sea; what they have of this continuity and integrity is owing to the growth of the valuable plant already named, for its roots spread amongst and bind together the sand, and its 'bents' (stalks) check the devastating action of the wind. Placed thus in unstable equilibrium, the state of the sand-hills at any moment expresses the balance of the integral effects of the sea-wind and vegetation, and from time to time this balance is unfavourable to the safety of the inland country; for the wind often conquers the marram, by heaping up sand more abundantly where this plant grows the best; inequalities are thus occasioned; tempests succeed; the relatively depressed parts of the sandy chain yield to the wind, receive the spray, and admit unusually elevated waves of the sea. 'Gaps' or 'breaches' (fearful name!) are thus generated; the ocean, swelled by north-west winds, rushes in; the internal rivers are choked by the simultaneous flooding of the Yare with salt water; the marshes are drowned, and years pass before the soil recovers its natural state."

The manner in which Dr. Smith succeeded in conquering this fearful state of things, as it existed in 1801, when the breaches in the line of sand-hills amounted altogether to one mile in length,-by imitating the natural embankments thrown up by the sea on the same shore, though most important as an operation of engineering, is foreign to our present subject, regarded as one of science. It is described in the Memoirs just cited, pp. 50-54.

Of the two alternating processes described by Professor Phillips, Sir C. Lyell, from his own observations and those of Mr. R. C. Taylor, has related some facts which are particular instances; of which those consisting in the restraint by the sand-dunes of the incursions of the ocean, have been already stated above; while the following show some additional consequences of the submersion of the barrier they form, and also in what manner the production of dunes is carried on in some localities of the same coast, simultaneously with the encroachment of the sea upon the land, of which other examples will be given.

The ancient villages of Shipden, Wimpwell, and Eccles (already mentioned) have disappeared; several manors and large portions of neighbouring parishes having, piece after piece, been swallowed up; nor has there been any intermission, from time immemorial, in the ravages of the sea along a line of coast twenty miles in length, in which these places stood. When Sir C. Lyell visited Eccles in 1839, the sea was fast encroaching on the sand-hills, and had laid open on the beach the foundations of a house, the upper part of which had evidently been pulled down before it had been buried under the sand. There are records of nine breaches, from 20 to 120 yards wide, having been made through the dunes between Eccles and Winterton noticed above, by which immense damage was done to the low grounds in the interior. An inland cliff, about a mile long, at Winterton, shows clearly that at that point the sea must have penetrated formerly farther than at present. But when the sufficiency of the meals and dunes securely to protect the harbours of Cley and Wells, and others, is affirmed to be dependent on "the present set of the tides," and is cited as affording a clear proof that it is not the strength of the material at particular points that determines whether the sea shall be progressive or stationary, but the general contour of the coast," '-we conceive that the resisting agency of the objects and process forming the particular subjects of this article, is greatly underrated; while we are precluded from admitting the conclusion to be altogether true, even with respect to secular periods, by the fact of that secular change in the contour of coastlines which is constantly in progress, and which Sir C. Lyell has himself evinced to play so important a part in historical physical geography.

Mr. R. C. Taylor has also described the dunes of South Wales, and some attendant phenomena (Phil. Mag.,' 2nd series, vol. i. p. 427). The tides on this coast attain a great elevation. The marshes of Pembrey in Caermarthenshire have four or five concentric ridges of sand-hills, forming as perfect and permanent barriers against the sea as the art of man could execute. The mouth of the river Ogmore, in Glamorganshire, presented in 1827 a singular appearance of desolation, through the agency of the wind and sand. Its ancient channel was filled up for two miles, houses were rendered uninhabitable, and sand-hills were

raised to the height of nearly 150 feet. "The mountains which bound the harbour," Mr. Taylor observed at that time, "will check the advance of this sand-flood into the interior, otherwise it threatens to overwhelm all the lands which adjoin it; while the squalls of wind, rushing down the steep valleys, occasion eddies, which deposit the sand at an elevation apparently far beyond the reach of such an irresistible enemy."

Much information respecting the sand-dunes of Cornwall, their encroachment on the land, and its counteraction by the use of the Arundo arenaria, will be found in the 'Parochial History' of that county by the late Mr. Davies Gilbert, P.R.S., and in the late Messrs. Lysons's Magna Britannia.'

"M. Elie de Beaumont [in his Géologie Pratique,' p. 218] has suggested that sand-dunes in Holland and other countries may serve as natural chronometers, by which the date of the existing continents may be ascertained. The sands, he says, are continually blown inland by the force of the winds, and by observing the rate of their march we may calculate the period when the movement commenced." On this, Sir C. Lyell, whose Principles' we are again citing, observes "But the example just given [that of Eccles] will satisfy every geologist that we cannot ascertain the starting point of dunes, all coasts being liable to waste, and the shores of the Low Countries in particular being not only exposed to inroads of the sea, but, as M. de Beaumont himself has well shown, having, even in historical times undergone a change of level. The dunes may indeed, in some cases, be made use of as chronometers, to enable us to assign a minimum of antiquity to existing coast-lines; but this test must be applied with great caution, so variable is the rate at which sands may advance into the interior." Dr. Boué has pointed to sandy sea-beaches as being the only formations now in progress, which are similar to deserts. [DESERTS.] If the latter have been produced by the gradual extension of the former, we may probably conclude that the permanent accumulation of sand was effected by the continual successive formation of dunes. In all past ages of the earth's physical history, as at the present era, they must have been formed wherever there was sea, together with rocks, the disintegration of which would afford the requisite material, if the form of coast-line, and the nature of its vegetable productions, and the prevalent direction of the winds were also favourable. And accordingly, sandstones of almost every geological age might be referred to containing vestiges of organic matter, lineally disposed, which may have resulted from their consolidation. These are more evident, however, in the later secondary and in the tertiary strata than in sandstones of great comparative antiquity; as might naturally be expected, from the longer exposure of the latter to metamorphic action, and the gradual obliteration of organic impressions by the various processes of alteration in rocks, the operation of which is permitted by the lapse of time. DUNG. [MANURE.]

DUODECIMALS, a term applied to an arithmetical method of ascertaining the number of square feet and square inches in a rectangu lar space whose sides are given in feet and inches. For instance, to find the contents of 6 feet 7 inches by 2 feet 5 inches, proceed as follows:

:

from the archbishop to the crown in council. It seems to have been called double querele, because in its form it is a complaint both against the judge and against the party at whose suit justice is delayed. (Blackst. Comm.,' Mr. Kerr's edit., iii. 256.) DUPLICATE RATIO (xóyos dinλaσíwv), a term used by Euclid, and defined as follows: If A be to B in the same proportion as B to c, then the ratio of a to c is called the duplicate ratio of A to B. When A, B, and c are lines, the duplicate ratio of A to B is that of the square on A to the square on B; when numbers, that of A times A to B times B. [RATIO; EXPONENT.] DUPLICATION OF THE CUBE, the solution of the following problem to find the side of a cube which shall be double that of another cube. This question, which is insoluble with perfect exactness by the methods of ordinary geometry, attained such a degree of notoriety among the Greek geometers that its origin was the subject of a mythologic fable. Eutocius, in his commentary on the sphere and cylinder of Archimedes, has preserved a letter of Eratosthenes to Ptolemy (Euergetes) in which it is said that one of the tragedians (Euripides, according to Valckenaer, cited by Montucla's editor) had introduced Minos erecting a sepulchre to Glaucus. The architect proposed one hundred palms every way, on which Minos declared that such a size would be too small for a royal sepulchre, and required that it should be doubled in size; and thereupon arose the difficulty. Eratosthenes also states another fable, namely, that the Delians, during a pestilence, had been ordered by the oracle to produce a cubical altar double of one which then existed. They applied to the school of Plato at Athens, who found that the problem eluded all their efforts. Other writers make mention of the latter story, and Valerius Maximus, in particular, adds that Plato referred the querists to Euclid; which must be an anachronism. However this may be, the problem continued to furnish an unceasing object of research; and such was the importance of its solution in the eyes of Eratosthenes, that he hung up his own solution in a temple as an offering, and composed an epigram, of which the principal value now is the proof which it affords that he considered Memechmus as the first inventor of the conic sections. Hippocrates of Chios, known as the first who could find the area of a (not any) curvilinear figure, perceived, according to Eratosthenes, that this problem could be solved as soon as two mean proportionals could be found between the side of the given cube and twice its length; that is, a being the length of the given cube, and x and y two lines such that

A: X: X Y and x: Y :: Y : 2 A,

this geometer saw that x was the side of the cube double of that on a. But the new problem presented exactly the same difficulty as before; various mechanical curves (as they were called) were invented for the purpose; it was found that the conic sections were sufficient, but no solution appeared consistent with the restrictions implied in the postulates of Euclid. Eutocius has mentioned the solution of Eudoxus, and has preserved those of Plato, Hero, Philo, Apollonius, Diocles, Pappus, Sporus, Menæchmus, Archytas, Eratosthenes, and Nicomedes. Pappus himself (in the third book, the first of those which remain entire) has preserved the solutions of Eratosthenes, Nicomedes, and Hero. In several instances these notices are the only clue which we have to the dates of the investigators, as there is strong presumption that those who are named by Eutocius and not by Pappus lived between the two. The trisection of the angle [TRISECTION] offered difficulties of a similar kind, and engaged the attention of several of the individuals above mentioned. That of the quadrature of the circle is altogether of another kind. For the various solutions of the problem of the duplication, see Montucla, 'Histoire des Recherches sur la Quadrature du Cercle,' 2nd edition, Paris, 1831; or Reimer, 'Historia Problematis de Cubi Duplicatione,' Göttingen, 1798; or the works of Eutocius and Pappus already cited.

The importance of this problem declined with the rise of the decimal arithmetic. Many different attempts were made, some avowedly mechanical (as opposed to geometrical), others by those who imagined they could overcome the original difficulty. Any process for the solution was called mesolabum (a term as old as Vitruvius). One of the last was that of the celebrated Vieta, containing an error, which is the more remarkable, that little, if any, notice has ever been taken of it. (See his works, Schooten's edition, p. 273.)

DUST, ATMOSPHERIC; DUST-HAZE; DUST-STORM; are terms designating related phenomena, depending on the suspension in the air of congeries of solid particles, which, within about a quarter of a century past have received some definite scientific attention; finelydivided solid matter, derived from the mineral kingdom, together with minute organisms or fragments of animal and vegetable origin, having come to be regarded as forming a proximate element of the lower strata of the atmosphere, regarded in the gross. Their suspension, no doubt, is dependent on the principle of the internal friction of the air, to which Professor Stokes has referred that of the clouds. [CLOUD.] The great pioneer of systematic and scientific micrology, Professor Ehrenberg of Berlin, who has done for a host of the objects of natural history requiring the microscope for their investigation, or even distinct vision, nearly what Linnæus did for all the species of organic nature known to him, which could be examined by the unassisted, or

but slightly assisted, eye, has not omitted to extend his philosophic scrutiny and distribution to the motes that float in the air, referring them to their places in nature, or to the creatures from which they have been derived. In 1849, he published collectively the results of the researches on this subject which he had then been pursuing for some years, under the title of 'Dust of the Regular-Winds and Bloodrains,' &c., consisting of 192 folio pages, and containing seven tabular catalogues, and six coloured plates of particles of atmospheric dust as viewed by the microscope. A synopsis of the contents of this work will be found in the Pharmaceutical Journal,' edited by the late Jacob Bell, for June 1850, vol. ix., pp. 569-575. From this it appears that the dust of the regular winds yields to chemical examination-silica, alumina, potash, soda, oxide of iron, oxide of manganese, oxide of copper, carbonate of lime, magnesia, water, and organic (combustible) bodies. By microscopic analysis are discerned in it fine quartz sand, still finer yellowish or reddish mould (very fine granular dust, Gallionella ferruginea ?), mixed with numerous organic forms and fragments. Generally single isolated fragments of pumice are observed in it, but chiefly green prismatic crystals, as in volcanic tufa and rapilli. Likewise white calcareous crystals which readily dissolve in muriatic acid. The organic substances are Polygastrica, Phytolitharia, Polythalamia, and soft vegetable parts. The total number of organic forms observed at this period amounted to 320 species; but many more have since been discovered, and have been described in Professor Ehrenberg's communications to the Royal Academy of Sciences at Berlin, continuing the elaborate investigation of which we here present merely a few results.

Over the island of Teneriffe, as recorded in Professor C. Piazzi Smyth's Report on the astronomical experiment in that locality, in the year 1856-the principal object of which was to ascertain, by following out a suggestion of Newton, how much celestial observation can be benefited by eliminating the lower third or fourth parts of the atmosphere-the existence of atmospheric dust is manifested in a remarkble manner, affecting all the phenomena dependent on the transparency and the transcalescence of the air. When describing the astronomical qualities of the atmosphere at his observing stations on the Peak, and after noticing those arising from the winds and the clouds, he thus describes those which are imparted by the dust: "A more important quality of the atmosphere was caused by the dust-haze, which was ever more or less present, though sometimes in vastly greater quantities than at others, and was precisely that which injured, or rendered impossible, daylight observations of stars (weakening direct light and multiplying general light). Where this dust-haze came from or went we could never tell; but, when present, we could easily distinguish its banks, or strata-dense strata, far above the clouds of the north-east trade-wind-as they stretched away and condensed in perspective towards the horizon. There were often several strata, one above the other, and mutually separated by very clear and sharplydefined spaces of atmosphere. When, as was sometimes the case, the summits of Grand Canary, or of Palma [other islands of the group], rising high above the sea of clouds, pierced also these upper strata of dust-haze, we had from [the observing station of] Guajara, the curious phenomenon of zones of blue mountain alternately distinct and again indistinct almost to invisibility, and yet no cloud or other recognised impurity of the atmosphere intervened. Being above much of this dust, though perhaps not the greater part of it [the elevation of the station being 8903 feet, and the dust-strata rising to not less than 11,000 feet], we were evidently better off than an observer at the level of the sea, when pointing to a zenith object, but for a horizontal one we were worse off, from often being in, and then looking through the whole plane of the stratum, and so experiencing the maximum of its light-stopping effect. Hence the occasional deterioration of sunrise and sunset were infinitely greater than anything that occurred at noon; and on some days, when the sky was perfectly free from cloud, and the sun had been distressingly hot and bright when high in the sky, yet it had almost become invisible before it set. It was seen, though made out with difficulty on such occasions, through a darkling, yet luminous haze of dull lemon-yellow colour; but what it set behind, or when exactly it did set, there was no ascertaining. The next evening perhaps the atmospheric dust had removed, and the change in the sunset was magical. The orb radiated hot and bright up to the moment of going down. Then, too, in place of the uniform yellow colour of the dusty sunset, the most gorgeous scarlets, yellows, and blues took its place."

From his experiments on the radiation of the sun, Professor Smyth says on this subject, after drawing some important inferences, Towards the chief astronomical end of the expedition, there is a yet more interesting conclusion to be drawn. The days of highest radiation are those of least temperature, and vice versû: and this difference obtains in a signal degree when there was no visible disturbing action of wind or clouds. What then causes the radiation of one day to be greater than that of another, and the temperature less? The immediate agent appears to be the atmospheric dust," diminishing by its interposition the effect of the solar radiation, but at the same time augmenting the temperature of the air by the multiplied radiation and reflection from its particles, in a manner corresponding to its action upon light as already noticed. "Hence then, we may easily understand why the small difference of altitude [1800 feet] between Alta

Vista [the upper observing station], and Guajara produced as great an increase in the radiation as did the great difference, nearly four times as great, between Guajara" itself, and the town of Oratava at the base of the mountain. "To eliminate this dusty medium" Professor Smyth concludes, "would be of the utmost consequence to the further improvement of astronomical observation, and may be considered the greatest and most subtile difficulty which the observer has to deal with; and it is probably general over the world, as on the South African mountains, at heights of 5600 feet, the phenomenon was almost at notable as on Guajara. From Dr. Mason's observations of solar radiation in Madeira, and from the relations given to me by inhabitants of Teneriffe, as to the periods of the year when the Peak is seen most clearly, I am disposed to think that there is least of this dust in the atmosphere in the latter end of the winter and the earlier part of the spring." (Report, or Phil. Trans., 1858, pp. 481, 482, 486-488, 499.) Professor Smyth found it almost impossible to collect particles of the dust-haze for examination. Some of it, however, deposited at Guajara, he found to be scales from butterflies' wings. He also obtained a specimen of atmospheric, dust which had fallen all over the Canarian islands, and another which had fallen at sea. By the microscopical examination of these, with a power of 400 linear, hardly anything could be made out but particles of sand. 'The colour of either was mostly an ochry yellow with an occasional bright red, more rarely a green fragment; but nothing organic could be clearly distinguished of a diatomaceous character; the forms of almost all the particles being like quartz rocks in miniature." (Report,' pp. 570,571.) From its characters and the concomitant phenomena, it may be inferred that the haze described in the following extract from Dr. Joseph D. Hooker's 'Himalayan Journals' (vol. ii. p. 409), is the dusthaze, occurring at altitudes in the Himalaya, nearly corresponding to those at which it exists, as we have seen, over the island of Teneriffe, and on the mountains of South Africa. "Two phenomena particularly obstruct radiation in Sikkim-the clouds and fog from the end of May till October, and the haze from February till May. Two months alone are usually clear; one before and one after the rains, when the air, though still humid, is transparent. The haze has never been fully explained, though a well-known phenomenon. On the plains of India, at the foot of the hills, it begins generally in the forenoon of the cold season, with the rise of the west wind; and, in February especially, obscures the sun's disc by noon; frequently it lasts throughout the twenty-four hours, and is usually accompanied by great dryness of the atmosphere. It gradually diminishes in ascending, and I have never experienced it at 10,000 feet; at 7000, however, it very often, in April, obscures the snowy ranges thirty miles off, which are bright and defined at sunrise, and either pale away, or become of a lurid yellow-red, according to the density of this haze, till they disappear at I believe it always accompanies a south-west wind (which is a deflected current of the north-west) and dry atmosphere in Sikkim." Hermann Schlagintweit has noticed the diminution of the solar radiation by the dust-storms of India, and observed a peculiar coloration of the sun, which he thinks is their regular concomitant when the air has lost a certain amount of transparency. In dust storms," he remarks, "the sky has," as in fogs, a decidedly reddish colour, which in this case is that of the dust itself, but the sun's disc is blue, a phenomenon evidently connected with the suspension of solid particles in the air. I observed this colour best on the 6th of April 1856, at Futtehpore. The hot wind lasted from 12h. 45m. to 6h. 10m. p.m., and stopped very suddenly after sunset. The sun was very much obscured as early as 1 p.m., and had then assumed this blue appearance so decidedly, that it looked like the sun's disc seen through a dark-blue glass; the shadow of a thin cylinder falling on white paper was nevertheless well defined and reddish, showing that the illuminated paper had received rays of the (complementary) bluish colour. The blue colour of the sun, though the light was gradually diminished, lasted until 5h. 19m. p.m., when the sun had a height only of about 15 degrees; then the disc soon disappeared entirely behind the clouds of dust. The temperature of the air diminished with the increase of the wind and discoloration of the air." (Journ. of the Asiat. Soc. of Bengal,' vol xxv., 1856, pp. 564, 565.) Whatever dependence, however, the blue colour of the sun may have upon the presence of solid particles in such cases, its cause, in other instances, is certainly a particular condition of the aqueous vapour in the air. [METEORS; METEOROLOGY; VOLCANOES; WINDS.] DUTCH LIQUID. [ETHYLINE.]

10 a.m.

DUTY. [RIGHT.]

DUUMVIRI, the name given to various magistrates in the republic of Rome, as well as in the colonia and municipia, who were elected in pairs for the discharge of any class of duties. We find the name applied to six different sets of functionaries at different periods. The first duumvirate on record was composed of the two judges of blood (duumviri perduellionis), appointed by Tullus Hostilius for the trial of P. Horatius, indicted for the murder of his sister, a crime of so great a nature as to be deserving of capital punishment (perduellio). The criminal condemned to death, as the lictor appeared with the fatal cord, claimed his right of appeal to the people, which being allowed

him, he was acquitted, as Livy says, by them, "admiratione magis virtutis quam jure causæ." (Liv. i. 26.) This office was exercised by Tarquinius Superbus alone, for tyrannical purposus (Liv. i. 49), and afterwards by the consuls (Liv. ii. 5), who were indeed a duumvirate. Whether these duumviri were the same as the quastores parricidii, as Niebuhr supposes, or whether they were distinct official personages during the kingly dynasty, is a question involved in the same obscurity as most other points relating to this period of Roman history. It certainly would appear that the two terms are confounded by ancient writers, some calling the judges appointed to preside at the trial of capital offences quæst. parric. others calling them duum. perduel. (cf. Liv. i. 26, d. 1, 2, 2, 23, and Festus sub voc. parici et sororium). But there is no doubt that they were distinct officials after the fall of the kingly power, and in the republican times, for while the one set, the quæstores, were regularly appointed by the year, the others were rarely and only on great occasions summoned to work. (cf. Liv. ii. 41, vi. 20; Dion Cass. xxxvii. 27; Aul. Gel. xvii. 21, and Cic. Pro Rabicio, c. iv. 2.) The duumviri sacrorum, who took care of and interpreted the Sibylline Books, were also a very ancient magistracy, ascribed by the old legends to the last Tarquin, and summoned into being on such dreadful emergencies as Livy records. (Liv. iv. 21.) Niebuhr thinks (Hist. of Rome,' i. p. 504, Engl. tr.) that the number was dictated by a wish to deal evenly with the first two tribes, the Ramnes and the Tities. Besides these there were the duumviri jure dicundo, who were the highest magistrates in the municipal towns and colonies (cf. Cie. Agr. Leg. ii. 34, D. 2, 3, D. 15, 1. 3, § ult. D. 47, 10, 13, 5), sometimes called consuls (Cic. in Pison. cxi.), and sometimes even dietator and quæstor. Their jurisdiction, according to Savigny, was, under the republic, unlimited in civil matters, but was restricted within the limits mentioned in the digest and code in Imperial times. The duumviri quinquennales, or the censors in the municipal towns; distinct personages from the above magistrates; the duumviri specially appointed for the purpose of building or dedicating temples (Liv. i. 28, xxii. 33); and the duumviri_navales, who were two officers, first elected in the year 436 A.U.C. (Liv. 'Epit.' lib. xii.; Niebuhr's Römische Geschichte,' translated by W. Smith and L. Schmitz, edit. 1851, vol. iii. p. 241.) Their duty was to collect, equip, man, and command the fleets of the republic. (Liv. ix. 30; xl. 18 and 26.) At the time of the first Runic war the office no longer existed. DWARF is a technical term employed by gardeners to distinguish fruit-trees whose branches proceed from close to the ground from riders or standards whose original stocks are several feet in height. DWARFING TREES. Nature, in many respects, can be made to deviate from her ordinary course of procedure, in order to be subservient to the purposes of men. In nothing is this fact more apparent than in the various modes of dwarfing trees.

The trees of our orchards and forests, for example, which grow naturally to a considerable size, can be made to assume all the appearances of maturity and age while only a few feet high; a forest in miniature can thus be created, which has a very grotesque and curious appearance. There are various methods of producing this effect; such as selecting peculiar kinds of stocks and grafting upon them. For example, if the pear-tree be grafted upon the quince stock, or the peach upon the plum, their growth is very much retarded, and their ultimate size is comparatively small; the same effect is produced upon all other trees where there is a difference between the tissue of the stock and that of the scion which has been grafted upon it; or if dwarf varieties be grafted upon stocks of a similar constitution, though taller in growth, the former will still retain their original character. Again, if the branches be bent, and the flow of the sap in any way impeded, or if a quantity of the fibrous roots be cut away, and nourishment more sparingly supplied to the branches, we arrive at the same results.

Sometimes trees are dwarfed by very severe pruning, particularly if this operation be performed in summer; and, although they evidently try for a length of time to overcome this obstruction to their natural size, yet they eventually assume a dwarfed and stunted habit, which, with a little care, may be retained for many years. The Chinese in particular have carried this practice to a great extent, and they ornament their fanciful gardens with miniature forests of elms, junipers, and other timber trees.

The methods of dwarfing employed by the Chinese are the following: young trees of various sorts are planted in flat porcelain vessels, and receive only so much water as is sufficient to keep them alive; in a very short time the pots are completely filled with roots, which, being hemmed in on all sides, cannot obtain a sufficient quantity of nutriment, and, as a matter of course, the growth of the stem and branches is thus impeded. The Chinese also pinch off the ends from the young shoots, mutilate the roots, lacerate the bark, tie down the branches, and break many of them half through; in short, by every means in their power they contrive to check growth, so that, stunted and deformed by these means, the trees soon assume all the marks of age when only two or three feet high.

There is another method of producing dwarf trees, which may be termed accidental: namely, selecting dwarf individuals and obtaining seed from them. It is well known that when the young seed is fertilised by the influence of the pollen belonging to its own flower, or to the same plant upon which it grows, the future progeny so produced partakes generally in a large degree of the nature of the parent from

which it originates. Now, if seed be carefully obtained from a variety rather more dwarf than usual, some of the plants produced by that seed will be somewhat more dwarf than their parents. The most dwarfed individuals again selected for seed will originate a race yet more dwarf than themselves; and thus, with patience and by successive generations, a variety only a few inches high may be obtained from a species two or three feet high, or even higher. This is the origin of dwarf roses, dahlias, and other common cultivated flowers. With the exception of this last-mentioned, method, all the others, however different they may seem, proceed from the same principle; for whether we graft upon stocks whose tissue differs in organisation from the scion, or whether we bend the branches, or cut or confine the roots, we prevent the full flow of the sap in all such cases, and thus advance the age of puberty and bring on a fruit-bearing state. When plants have arrived at this stage of existence, all their energies are directed to the formation of fruit; hence forcing a tree into an early state of fruit bearing is almost synonymous with dwarfing it.

DYEING is the art of staining textile substances with permanent colours. To cover their surfaces with colouring matters removable by daily use would be to apply a pigment rather than to communicate a dye. Dye-stuffs can penetrate the minute pores of vegetable and animal fibres only when presented to them in a state of solution, and they can constitute fast colours only by passing afterwards into the state of insoluble compounds with the fibres themselves. Dyeing thus appears to be altogether a chemical process, and to require for its due explanation and practice an acquaintance with the properties of the elementary bodies, and the laws which regulate their combinations. It is true, nevertheless, that many operations of this, as of other chemical arts, have been practised from the most ancient times, long before any just views were entertained of the nature of the changes that took place. Mankind, equally in the rudest and most refined state, have always sought to gratify the love of distinction by staining their dress, sometimes even their skin, with gaudy colours. Moses speaks of raiment dyed blue, and purple, and scarlet, and of sheepskins dyed red,-circumstances which indicate no small degree of tinctorial skill. He enjoins purple stuffs for the works of the tabernacle and the vestments of the high priest. In the article CALICO PRINTING we have shown from Pliny that the ancient Egyptians cultivated that art with some degree of scientific precision: seeing that they knew the use of mordants, or of those substances which, though they may impart no colour themselves, yet enable white cloth to absorb colouring drugs. Tyre, however, was the nation of antiquity which made dyeing its chief occupation and the staple of its commerce. There is little doubt that purple, the sacred symbol of royal and sacerdotal dignity, was a colour discovered in that city, and that the discovery and use of the dye contributed to the opulence and grandeur of the place. Homer marks the value as well as antiquity of this dye, by describing his heroes as arrayed in purple robes. Purple habits are mentioned among the presents made to Gideon by the Israelites from the spoils of the kings of Midian. The juice employed for communicating this dye was obtained from two different kinds of shell-fish, described by Pliny under the names of purpura and buccinum; and was extracted from a small vessel, or sac, in their throats, to the amount of only one drop from each animal. A darker and inferior colour was also procured by crushing the whole substance of the buccinum. A certain quantity of the juice collected from a vast number of shells being treated with sea-salt, was allowed to ripen for three days; after which it was diluted with five times its bulk of water, kept at a moderate heat for six days more, occasionally skimmed to separate the animal membranes, and when thus clarified was applied directly as a dye to white wool, previously prepared for this purpose by the action of lime-water, or of a species of lichen called fucus. Two operations were requisite to communicate the finest Tyrian purple: the first consisted in plunging the wool into the juice of the purpura; the second, into that of the buccinum. Fifty drachms of wool required one hundred of the former liquor, and two hundred of the latter. Sometimes a preliminary tint was given with coccus, the kermes of the present day, and the cloth received merely a finish from the precious animal juice. The colours, though probably not nearly so brilliant as those producible by our cochineal, seem to have been very durable, for Plutarch says, in his Life of Alexander' (chap. 36), that the Greeks found in the treasury of the King of Persia a large quantity of purple cloth, which was as beautiful as at first, though it was 190 years old. The difficulty of collecting the purple juice, and the tedious complication of the dyeing process, made the purple wool of Tyre so expensive at Rome that in the time of Augustus a pound of it cost nearly 301. of our money. Notwithstanding this enormous price, such was the wealth accumulated in that capital, that many of its leading citizens decorated themselves in purple attire, till the emperors arrogated to themselves the privilege of wearing purple, and prohibited its use to every other person. This prohibition so much discouraged the art of dyeing purple as eventually to occasion its extinction, first in the western and then in the eastern empire, where, however, it existed in certain imperial manufactories till the 11th century.

Dyeing was little cultivated in ancient Greece. The people of Athens wore, generally, woollen dresses of the natural colour. But the Romans

must have bestowed some pains upon this art. In the games of the circus, parties were distinguished by colours. Four of these are described by Pliny,-the green, the orange, the gray, and the white. The following ingredients were used by their dyers: a crude native alum mixed with copperas, copperas itself, blue vitriol, alkanet, lichen rocellus or archil, broom, madder, woad, nut-galls, the seeds of pomegranate, and of an Egyptian acacia.

The moderns have obtained from the New World several dye-drugs unknown to the ancients, such as cochineal, quercitron, Brazil wood, logwood, annatto, &c.; and they have discovered the art of using indigo as a dye, which the Romans knew only as a pigment. But the vast superiority of our dyes over those of former times must be ascribed principally to the employment of pure alum and solution of tin as mordants, either alone or mixed with other bases; substances which give to our common dye-stuffs remarkable depth, durability, and lustre. Another improvement in dyeing of more recent date is the application to textile substances of metallic compounds, such as Prussian blue, chrome yellow, manganese brown, &c.

Indigo, the innoxious and beautiful product of an interesting tribe of tropical plants, which is adapted to form the most useful and substantial of all dyes, was actually denounced as a dangerous drug, and forbidden to be used, by our parliament in the reign of Queen Elizabeth. An Act was passed authorising searchers to burn both it and logwood in every dye-house where they could be found. This Act remained in full force till the time of Charles II.; that is, for a great part of a century. The purpose of this statute was professedly to check the use of two dye-drugs supposed to be dangerous; but it is probable that the legislation was suggested by the growers or makers of certain English drugs, to favour their monopoly.

Mr. Delaval made many ingenious experiments to prove that the particles of dye-stuffs possess no power of reflecting light, and that, therefore, when viewed upon a dark ground, they all appear black, whatever colour they may exhibit when seen by light transmitted through them. He hence inferred that the difference of colour shown by dyed cloths is owing to the white light which is reflected from the textile fibres being decomposed in its passage through the superinduced colouring particles. We think it more than probable that this conclusion is in some respects incorrect, and that the aluminous, iron, and tin bases form combinations with dye-stuffs which are capable of reflecting light, independent of the reflection from the fibre itself. There can be no doubt, however, that this latter reflected light adds greatly to the brightness of the tints, and that the whiter the textile substance is, the better dye it will, generally speaking, receive. It is for this reason that scouring or bleaching of the stuffs is usually prescribed as a process preliminary to dyeing.

Bergman appears to have been the first who referred to chemical affinities the phenomena of dyeing. Having plunged wool and silk into two separate vessels, containing solution of indigo in sulphuric acid diluted with a great deal of water, he observed that the wool abstracted much of the colouring matter, and took a deep blue tint, but that the silk was hardly changed. He ascribed this difference to the greater affinity subsisting between the particles of sulphate of indigo and wool, than between these and silk; and he showed that the affinity of the wool is sufficiently energetic to render the solution colourless by attracting the whole of the indigo, while that of the silk can separate only a little of it. He thence concluded that dyes owed both their permanence and their depth to the intensity of that attractive force.

We have therefore to consider in dyeing the play of affinities between the liquid medium in which the dye is dissolved and the fibrous substance to be dyed. When wool is plunged in a solution containing cochineal, tartar, and salt of tin, it readily assumes a beautiful scarlet hue; but when cotton is subjected to the same bath it receives only a feeble pink tinge. Dufay took a piece of cloth woven of woollen warp and cotton weft, and having exposed it to the fullingmill in order that both kinds of fibre might receive the same treatment, he then subjected it to the scarlet dye; he found that the woollen threads became of a vivid red, while the cotton continued white. By studying these differences of affinity, and by varying the preparations and processes, with the same or different dye-stuffs, we may obtain an indefinite variety of colours of variable solidity and depth of shade.

Dye-stuffs, whether of vegetable or animal origin, though susceptible of solution in water, and, in this state, of penetrating the pores of fibrous bodies, seldom possess alone the power of fixing their particle so durably as to be capable of resisting the action of water, light, and air. For this purpose they require to be aided by another class of bodies, already alluded to, which bodies may not possess any colour in themselves, but serve in this case merely as a bond of union between the dye and the substance to be dyed. These bodies were supposed, in the infancy of the art, to seize the fibres by an agency analogous to that of the teeth of animals, and were hence called mordants, from the Latin verb mordere, to bite. But the term derived from it has gained such a footing in the language of the dyer that all writers upon his art are compelled to adopt it.

Mordants may be regarded, in general, as not only fixing but also occasionally modifying the dye, by forming with the colouring particles an insoluble compound, which is deposited within the textile fibres.

Such dyes as are capable of passing from the soluble into the insoluble state, and of thus becoming permanent, without the addition of a mordant, have been called substantive, and all the others have been called adjective colours. Indigo and tannin are perhaps the only dyes of organic origin to which the title substantive can be applied, and even they probably are so altered by atmospheric oxygen, in their fixation upon stuffs, as to form no exception to the true theory of mordants.

Mordants are of primary importance in dyeing; they enable us to vary the colours almost indefinitely with the same dye, to increase their lustre, and to give them a durability which they otherwise could not possess. A mordant is not always a simple agent; but in the mixture of which it consists various compounds may be formed, so that the substances may not act directly, but through a series of transformations. The China blue process [CALICO PRINTING] affords a fine illustration of this truth. Sometimes the mordant is mixed with the colouring matters; sometimes it is applied by itself first of all to the stuff; and at others both these methods are conjoined. We may dye successively with liquors containing different substances, which will act differently according to the different mordants successively employed. One solution will give up its base to the stuff only when aided by heat; another acts better and more uniformly when cold, though this is a rarer case.

When a mordant consists of a changeable metallic oxide, as of iron or tin, unless great nicety be used in its application, either no effect or an injurious one may be produced upon the dye. All these circumstances prove how necessary it is for the dyer to be thoroughly versed in chemical science. Each of the great dye-works in Alsace, celebrated for the beauty and fixity of their colours, is superintended in the laboratory department by a gentleman who has studied chemistry for two or more sessions in the universities of Paris or some other eminent schools. The English cotton dyers, twenty or thirty years ago, were far inferior in skill to those of France; but they have recently made great advances. Now many of the Manchester houses have chemists (some of them men of great attainments), and no doubt in other towns also; and for smaller establishments there are professional consulting chemists.

The first principle of dyeing fast colours, we have seen, consists in causing the colouring matter to undergo such a change, when deposited upon the wool or other stuffs, as to become insoluble in the liquor of the dye-bath. The more powerfully it resists the action of other external agents, the more solid or durable is the dye. Generally speaking, a piece of well-dyed cloth should not be materially affected by hot water, by soap and water, by exposure to air and light, by dilute nitric acid, or even by very dilute aqueous chlorine.

In the following details concerning the art of dyeing we shall consider principally its application to wool and silk, having already treated, in the article CALICO PRINTING, of what is peculiar to cotton and linen.

The operations to which wool and silk are subjected preparatory to being dyed are intended, 1, to separate certain foreign matters from the animal fibre; 2, to render it more apt to unite with such colouring particles as the dyer wishes to fix upon it, as also to take therefrom a more lively and agreeable tint, as well as to be less liable to soil in use. The matters foreign to the fibre are either such as are naturally associated with it during its production by the animal, such as have been added to it in the spinning and weaving operations, or such as have been accidentally applied.

Silk is scoured by means of boiling in soap and water, whereby it is freed from a varnish, improperly called gum. This consists of an azotised compound, which may be separated in a gelatinous form by cooling the hot water saturated with it. It constitutes about a fourth part of the weight of most raw silks, and contains a little colouring matter of an orange or yellow hue. When silk is required to be extremely white, either to be woven in that state, or to receive the brightest and purest dyes, it should be exposed to the action of humid sulphurous acid. For dark dyes, silk need not be scoured at all, in which case it preserves its whole weight. Wool is first washed in running water to separate its coarser impurities; it is then deprived of its yolk (a species of animal soap secreted from the skin of the sheep) either by che action of ammoniacal urine, by soap and water, or by a weak lye of carbonate of soda. Common wools lose in this way from 20 to 50 per cent. of their weight, and merino wools still more. They receive their final bleaching by the fumes of burning sulphur, or by aqueous sulphurous acid.

Wools present remarkable differences in their aptitude of combining with dye-stuffs, depending upon the different structure of the imbrications of the filaments. The colouring particles seem to insinuate themselves at these pores with greater or less facility, and to be retained with greater or less force, according to the magnitude and form of the orifices. This difference in dyeing, therefore, is not due to the repulsive action of fatty matter, as has been commonly supposed, since it still exists in wool even when every particle of grease has been removed from it by alcohol and ether. A boiling in a solution of bran is often had recourse to, in order to make wool take the dye more readily and equally; but a hot lye containing one half per cent. of crystallised carbonate of soda answers much better. When heated to the temperature of 140° or 150° Fahr., the wool should be immersed

in that liquor, and turned about for half an hour. The wool receives a faint yellowish tint from this bath, but it speedily becomes white on exposure to air; or it may be whitened at once by passing it through tepid water containing a very small quantity of muriatic acid. The yellow colour is most probably occasioned by the reaction of the sulphur and iron contained in the wool.

According to the experiments of Thenard and Roard, alum combines with wool in the state of a salt, without separation of its acid constituent. Wool boiled with a solution of tartar decomposes a portion of it completely; some of the acid and a little of the tartar combine with the wool, while a neutral tartrate of potash remains in the bath. This fact is interesting in reference to the scarlet dye, showing the important part which tartaric acid here performs.

Tinctorial colours are either simple or compound. The simple are black, brown or dun, blue, yellow, and red; the compound are gray, purple, green, orange; and other numerous modifications, all producible by the mixture of simple colours. We shall treat here of only black and brown, in the present place.

1. Black. If we apply to a white stuff blue, red, and yellow, in certain proportions, the resulting colour will be black. Proceeding on this principle, Castel asserted that 15 parts of blue, 5 of red, and 3 of yellow, will produce a perfect black; but in making this statement he was influenced rather by theoretical than practical considerations. In fact he has afforded us no means of procuring these simple colours in an absolute state. It is undoubtedly true, however, that red, yellow, and blue, employed in adequate quantities, will produce black: because they will together absorb, or obstruct the passage of all coloured light, or, in other words, cause its total privation, whence blackness must result. If we suppose a piece of cloth, to which these three colours have been communicated, but not in such proportions as to produce a pure black, we shall have a tint corresponding to the colour that is in excess; as, for example, a blue, violet, red, or greenish black; and with paler tints we shall have a bluish, violet, red, or greenish gray.

Gall-nuts, and a salt of iron, so generally employed for the black dye, give merely a violet or greenish-gray, and never a pure black. The pyrolignite of iron, which contains a brown empyreumatic matter, produces a brown inclining to greenish-yellow in light shades, and to chestnut-brown in dark hues. By galling cotton and silk, after a bath of pyrolignite of iron, and repeating the processes several times, a tolerably pure black may be procured. Galls, logwood, and a salt of iron (copperas) produce merely a very deep violet-blue; but if they be applied to wool in a hot bath, with frequent exposure to air, the logwood induces a brownness which is favourable to the formation of

black.

The black dye for hats is communicated by logwood, copperas, and verdigris mixed in certain proportions in the same bath; from that mixture there results a vast quantity of an ochreous muddy precipitate, amounting to 25 per cent. of the copperas employed. This mud forms a deposit upon the hats which not only corrodes the fine beaver filaments, but causes both them and the felt to turn speedily of a rusty brown. A well-dyed black hat should retain its original tint as long as it lasts,-a condition seldom realised. Beaver hats, however, to which these remarks refer, have been almost superseded by those covered with silk plush, to which a different process of dyeing applies.

Since gall-nuts give a blue precipitate with the peroxide salts of iron, they are occasionally replaced by sumach, bablah, &c.; but account should be taken in this substitution of the proportions of red or yellow colouring matter in these substances, relatively to the tannin which alone forms the blue precipitate. When a black of the best possible shade is to be given, the wool should be first grounded with indigo, then passed through a bath of logwood, sumach, and protosulphate-of iron (green copperas). Sumach and nut-galls may also be employed in the proportion of 6 to 24; or the sumach may be replaced by nut-galls, if they be equal to one-third of the sumach prescribed. A good black may be dyed upon an indigo ground with 100 lbs. of wool, by taking 200 lbs. of logwood, 60 lbs. of sumach, 24 lbs. of galls, and 20 lbs. of green copperas; and giving three heats of two hours each to the wool, with airings between. A good black, without an indigo blue ground, may be given to 100 lbs. of wool, by boiling it in a bath of 25 lbs. of alum and 674 of tartar; grounding it with weld and madder; then passing it through a bath of 200 lbs. of logwood, 60 of sumach, and 24 of galls; taking it out, adding to the bath 20 lbs. of copperas; lastly, giving it three heats of two hours each time.

The best French black, according to Hellot, may be given to wool by first dyeing it a dark blue in the indigo vat; then washing and fulling it; then, for every 50 lbs., putting into the copper 8 lbs. of bruised galls, and as much logwood tied up in a coarse canvas bag, and boiling thein for twelve hours. One-third of the bath thus prepared is to be transferred into another copper with 1 lb. of verdigris, and the wool or stuff is to be worked in this solution without intermission for two hours: the bath being kept hot, but not boiling. After taking out the stuff, another third part of the first bath is to be added along with 4 lbs. of green copperas; the fire must be lowered while this salt is being dissolved, and the bath being refreshed with a little cold water, the stuff is to be worked through it for half an hour, and then aired. Lastly, the residuary third of the first bath is to be now introduced, taking care to squeeze the contents of the bag. From 8 to 10 lbs. of