take its bearing separately by its own gravity, or by such farther pressure as may be deemed proper. When the rods have taken their bearing and settlement, a row of sloping rods have to be added to each side of the jetty, inclining inwards one foot in ten or twelve, to give lateral support; and at this state of the operation, it is proposed to key on to the rods the iron collars for the permanent support of the horizontal frames and the platform."

Captain Vetch estimates that the expense per lineal yard of a breakwater of this description would be 1487. 138. 8d., while the Plymouth breakwater cost about 1000l. per lineal yard, and the harbours of refuge, which it is in contemplation to erect on the coast of Kent, have been estimated to cost 6607.

There would also be an immense

saving in time:

"The Plymouth breakwater took twentyeight years to complete, and it is understood, fourteen years has been estimated as the required time for the harbour of refuge at Dover; now, in the construction by iron framing, it is reasonable to assume that a frame of four feet may be set each tide, and by working from two ends, sixteen feet per diem ought to be performed in good weather; the length of sea face of the proposed harbours of refuge average 9100 feet, so that 569 days would be required to complete the iron framing for one, and allowing for Sundays and bad weather, the work would be accomplished in less than three years, say in one-fifth of the time estimated for the Dover harbour, on the principle of construction of the breakwater in Plymouth Sound."

We have now before us the finishing volume of this magnus opus of the Useful Knowledge Society. We thought that it had been admitted on all hands-some considerable merits notwithstanding-to be a failure; but if the Committee of the Society, with Lord Brougham at its head, are to be believed, it leaves, on the contrary, little, if anything, to be desired! In a valedictory address from the Committee, which is prefixed to this last volume, it is described as a Cyclopædia "without any important omissions"'-a work which "may fairly take

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rank amongst works of authority, systematically conducted, without any improper abridgment of labour or expense ;" and this 66 although it is the cheapest original work of the class which any country has produced." The publisher of the Cyclopædia takes a flight still higher than his masters of the Committee, for he protests in a separate address of his own, that “the articles in many of the great branches of knowledge are regarded as authorities, and have acquired celebrity wherever the English language is read!" Only two slight specks in this brilliant picture are confessed to; one by the Committee, who say that "the limits proposed for this work have been exceeded by about one-fourth," and the other by Mr. Knight, who says that "the name of the Penny Cyclopædia was derived from its original issue in a weekly sheet, when a work of much less magnitude was contemplated;" but that the word "PENNY is now (to be) received as indicative only of its extreme cheapness."

We took no small pains at the commencement of this work to point out wherein it was deficient, and how it might be improved; and we shall not now shrink, at its conclusion, from stating openly what we think of these boastful pretensions. Verily, then, we think them a perfect disgrace to the parties from whom they emanate. The "limits exceeded by about one-fourth" only! As audacious a misstatement as ever was uttered or published. The "limits proposed for this work," as any person may satisfy himself by referring to the original Prospectus, were eight volumes. The actual number is twenty-seven. An increase of nineteen instead of two!

examination of the kernels within-if "improper abridgment of expense" there be none in lavishing money on garbage, and leaving nothing to pay for many of the most valuable products of the garden and field: yes, if system it be to allow to the first three letters of the alphabet three times the space allowed to any of the others—if system it be to begin with dividing a discourse into eight heads, and end with twenty-seventh and lastly. "Without any important omissions!" We should like to have but a silver groat for every 66 important omission" we could point out. To confine ourselves to the volume before us, there is not in the article "Weights and Measures," (in all other respects a very good treatise on the subject,) nor anywhere else in the Cyclopædia, any account of the new mode of measuring the tonnage of vessels, though manifestly a matter of the first importance, and established by an Act of Parliament, which is not of yesterday, but some five or six years old. Nor in that on "Woollen and Worsted Manufactures," and the "Processes" comprehended under it,-a word of the modern processes of Drying by Centrifugal Action, and Felting instead of Weaving. been so all through: scarcely an article can be mentioned which has not been quite as remarkable for what it did not contain, as for what it contained. Mr. Knight is pleased to say, that "the articles on many of the great branches of knowledge are regarded as authorities, and have acquired celebrity wherever the English language is read." Will Mr. Knight be so good as to specify what these "many articles" are? For ourselves, we must confess that we are in a state of absolute ignorance on the subject. But, then, there is the cheapness! Other Cyclopædias have been cheap; but this, according to both Committee and Publisher, is the cheapest of all! Cheapness is a term which must be guaged by the test of merit. To call an Encyclopædia a "Penny" one, is no more indicative of extreme cheapness" than it would be to call it a "Sixpenny" or a "Shilling" one. As there is such a thing as being "penny wise and pounds

It has

foolish," so is there such another thing as paying too dear for the (penny) whistle.” An article may be dear at a penny, which, if made of a better quality, would be cheap at a shilling. Now, what is it we ought to look for in a Cyclopædia? Is it not something on every thing-either full information on all matters of importance within the circle of human knowledge, or abbreviated notices, with references to the sources, where deeper draughts of instruction may be obtained? Tested by this standard, the Penny Cyclopædia is anything but a cheap work. We know of no work of the kind which, if consulted as a book of reference, is more likely to disappoint a reader. The information given is often exceedingly incomplete; rarely of the newest; now and then very erroneous; and, not seldom, amounts to just nothing at all. Surely something greatly better than this might have been expected for Ten Pounds the sum which the Penny Cyclopædia now costs in its complete state. Ten Pounds is no trifle, especially to persons of the middling and lower classes, for whose special benefit this work was stated to have been designed; nor would it be difficult to point out many ways in which such a sum might be laid out in the mart of literature to much greater advantage than in the purchase of penny-worths like this.

All that we have said of this Cyclopædia generally, is quite consistent with a cordial recognition of great merit in particular portions of it. The astronomical and mathematical, chemical and geographical departments, are by far the best executed; the mechanical and manufacturing (of which we are perhaps most competent to speak) among the worst. All that Airy, and De Morgan, and Phillips, and a few others of the same high stamp, could do to give reputation to the work has been done; but the shellfishmongers, the grub-catchers, the geologists, the philologists, and the Scotch lawyers, have been too many for them.

We give from the concluding volume before us a couple of specimens of the better sort. The first is from an article on the "Zenith Sector :"

ime

"When Troughton first proposed the mural circle as the best form for a meridian declination instrument, great doubt was thrown on the practicability of observing by reflection with sufficient nicety; and, in that case, as the mural circle does not reverse, a supplementary instrument was wanted to show the position of a zenith or horizon. Partly on this account, but chiefly to settle the constants of aberration and precession with the greatest precision, Troughton planned a zenith tube, consisting of a telescope of 25 feet focal length, without any sector, and in which the variations of zenith distance of y, Draconis, and close zenithal stars, were to be measured by a micrometer screw. The instrument has not been described; indeed it can searcely be considered as yet completed, though several improvements have been made in its construction by Mr. Airy, since his appointment as Astronomer Royal. The telescope rests on its lower end, continued beyond the focus, on a piece which has adjustment for verticality, and a collar below the object-glass is pressed by a spring into a Y bearing. The wires at the focus are moved by a micrometer screw, and the star and wires are seen through a diagonal four-glass eye-piece. The plumbline hangs within the tube, and is viewed above and below by micrometer microscopes. Instead of adjusting the plumb-line before each observation, it is bisected by the micrometers after the observation, and a correction applied, which is deduced from the upper and lower readings. Mr. Airy having had some reason to suspect that the wire twisted on reversing the instrument, has given a double suspension to the plumb-line, and made the instrument reversible on a star in the same night, by using a stop, as in the ordnance sector. The observations with the zenith-tube are printed yearly in the Greenwich Observations.

"The zenith sector has not been much used upon the Continent since the great surveys made in the middle of the last century for ascertaining the figure of the earth. In the French arc from Dunkirk to Formentera, the latitudes were observed by the repeating circle; and in some of the stations there is reason to suspect that error has been committed. More recently, the transit in the prime vertical has been employed in Germany and Russia, for ascertaining differences of latitude, and, as it would seem, with great success. A prime vertical transit has lately been constructed by Repsold, for the imperial observatory of Pultowa, of which a most favourable account has been given by Professor Struve. While admitting the excellence of this kind of instrument for telescopes of moderate size, we do not see

31

how they can equal, far less surpass, the zenith sector, when made reversible, and of the proper magnitude."

The next extract consists of a brief but interesting notice of the inventor of marmotinto-a curious art, which was in great vogue in the days of our grandfathers, but has long since gone entirely out of use:

ZOBEL, BENJAMIN, the inventor of marmotinto, was born in 1762, at Memmingen in Bavaria. He received his education at the government school of that city, and acquired the rudiments of drawing from one of the monks belonging to the convent of Ottobenern. In 1781, he went to Amsterdam, where he resided for two years occupying himself chiefly in portrait-painting. In 1783, he came to London, where he formed acquaintance with Morland and Schweickhardt, the latter of whom was employed at Windsor Castle, by George III's "table decker." It was then the custom to ornament the royal dinner table by having a silver plateau extending along the centre, on which were strewed various coloured sands or marble dust; in fanciful designs of fruit, flowers, arabesque work, &c. For this an artist of considerable talent and of great freedom of hand was required. On the retirement of Schweickhardt, Zobel was appointed; and he continued to fill the office for a considerable period. Ornamenting the royal table in the manner just described was a daily occupation, the sands not being cemented by any substance. From this occupation arose the idea in the mind of Zobel of producing a finished and permanent picture, by the use of some substance by which the sands might be fixed. After various experiments, a composition (in which gum-arabic and spirits of wine formed the chief ingredients) was found to answer the best. The subject of the picture having been designed either in panel or milled board, a coating of the glutinous substance was spread over it; the different coloured sands were then used in a similar manner as that employed in decking the royal table, viz. by strewing them from a piece of card held at various elevations, according to the strength or softness of the tint required. Thus was formed a picture, not subject to decay, and perfectly permanent in all its parts, and this was called by the inventor Marmotinto. Some of the best specimens of this peculiar art were formerly in the possession of the late Duke of York, but were sold, at his death, at Oatlands. Several are still among the collections of paintings belonging to the Duke of Northumberland, and Sir Willoughby Gordon,