MR. TALBOT'S PROCESSES OF PHOTOGENIC

DRAWING.

In

[Read at a late meeting of the Royal Society.] The subject naturally divides itself into two heads-the preparation of the paper, and the means of fixing the design. order to make what may be called ordinary photogenic paper, the author selects, in the first place, paper of a good firm quality, and smooth surface; and thinks, that none answers better than superfine writing paper. He dips it into a weak solution of common salt, and wipes it dry, by which the salt, is uni. formly distributed throughout its substance. He then spreads a solution of nitrate of silver on one surface only, and dries it at the fire. The solution should not be saturated, but six or eight times diluted with water. When dry, the paper is fit for use. He has found, by experiment, that there is a certain proportion between the quantity of salt and that of the solution of silver which answers best, and gives the maximum effect. If the strength of the salt is augmented beyond this point, the effect diminishes, and, in certain cases, becomes exceedingly small. This paper, if properly made, is very useful for all ordinary photogenic purposes. example, nothing can be more perfect than the images it gives of leaves and flowers, especially with a summer sun. The light passing through the leaves delineates every ramification of their nerves. If a sheet of paper, thus prepared, be taken and washed with a saturated solution of salt, and then dried, it will be found (especially if the paper has been kept some weeks before the trial is made), that its sensibility is greatly diminished, and, in some cases, seems quite extinct. But if it be again washed with a liberal quantity of the solution of silver, it becomes again sensible to light, and even more so than it was at first.

For

In this way,

by alternately washing the paper with salt and silver, and drying it between times, Mr. Talbot has succeeded in increasing its sensibility to the degree that is requisite for receiving the images of the camera obscura. In conducting this operation, it will be found, that the results are sometimes more, and sometimes less satisfactory, in consequence of small and accidental variations in the proportions employed. It happens sometimes that the chloride of silver is disposed to darken of itself, without any exposure to the light-this shows, that the attempt to give it sensibility has been carried too far. The object is, to approach to this condition as near as possible, without reaching it; so that the substance may be in a state ready to yield to the slightest extraneous force, such as the feeble impact of

the violet rays when much attenuated. Having, therefore, prepared a number of sheets of paper, slightly different from one another in the composition, let a piece be cut from each, and, having been duly marked or numbered, let them be placed side by side in a very weak diffused light, for about a quarter of an hour; then, if any one of them, as frequently happens, exhibits a marked advantage over its competitors, Mr. Talbot selects the paper which bears the corresponding number to be placed in the camera obscura.

With regard to the second object-that of fixing the images-Mr. Talbot observed, that, after having tried ammonia, and several other re-agents, with very imperfect success, the first which gave him a successful result, was the iodide of potassium, much diluted with water. If a photogenic picture is washed over with this liquid, an iodide of silver is formed, which is absolutely unalterable by sunshine. This process requires precaution; for, if the solution is too strong, it attacks the dark parts of the picture. It is requisite, therefore, to find, by trial, the proper proportions. The fixation of the pictures in this way, with proper management, is very beautiful and lasting. The specimen of lace, which Mr. Talbot exhibited to the Society, and which was made five years ago, was preserved in this manner. But his usual method of fixing is different from this, and somewhat simpler-or, at least, requiring less nicety. It consists in immersing the picture in a strong solution of common salt, and then wiping off the superfluous moisture, and drying it. It is sufficiently singular that the same substance which is so useful in giving sensibility to the paper, should also be capable, under other circumstances, of destroying it; but such is, nevertheless, the fact. Now, if the picture which has been thus washed and dried, is placed in the sun, the white parts colour themselves of a pale lilac tint, after which they become insensible. Numerous experiments have shown the author that the depth of this lilac tint varies according to the quantity of salt used, relatively to the quantity of silver; but by properly adjusting these, the images may, if desired, be retained of an absolute whiteness. He mentions, also, that those preserved by iodine are always of a very pale primrose yellow, which has the extraordinary and very remarkable property of turning to a full gaudy yellow, whenever it is exposed to the heat of a fire, and recovering its former colour again, when it is cold.-Athenæum.

Feb. 22nd.-The Converzatione.-There were some interesting specimens on the table of the rock salt of Cheshire, and of the several varieties of refined salt as prepared for the different markets, sent by Mr. Hemming. Mr. Palmer's pneumatic filter was exhibited. It will be unnecessary to notice it here, as it was described in a recent number of the Mechanics' Magazine. We will only observe, that though in most cases it will form a useful apparatus, still there is such a thing as making more haste than good speed. Good filtration cannot always be effected through the medium of pressure as a substitute for surface, but where it can be used with advantage, this is a ready and elegant mode of applying it.

The Lecture.-Mr. Johnstone lectured "" on the leading distinctions in the investigation of mental and material phenomena.' This is a subject which, to have justice done to it, would have required a mind of the highest order, and a larger allowance of time than could be afforded to a single lecture.

As thus treated, it would not have been inappropriate either to the occasion or to the character of the audience; but as treated by the lecturer it was an agreeable essay on the advantages and on some of the characteristics of metaphysical science, interspersed with pleasant remarks and quotations, and having just such a sprinkling of allusion to physical facts as would afford a colouring of justification of the title given to the lecture. The title was a misnomer also, in a yet more important particular, for the few leading distinctions" to which the lecturer adverted, referred to what is incidental to the subjects themselves, and not to discriminations in the mental process implied in their "investigation.'

In jus

tice to the lecturer it should be observed, that besides being compelled by the limitation of his time (the rule, which grants only an hour, being always strictly enforced) to give only fragmentary notices, as it were, of his subject, he was almost obliged to introduce physical illustrations, if merely to relieve the tedium of his theme, and even though it should require a most indulgent latitude of allowance to deem them as being at all relevant to it, in the manner at least, in which he treated it.

An abstract of the lecture would exceed our limits, and a complete syllabus would be uninteresting; we shall therefore give in the latter form only two of its heads,

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the first, on acount of the justness of the observations, and the second, to substantiate our criticism.

1. Physical science depends greatly as to its progress and its truthful character, on the mind's procedure in the investigation of its objects; hence the value of mental science, the utility of its culture, the futility of the ancient philosophy, the efficiency of the Baconian method, and the surprising advances which have followed its adoption. Ancient, was not less vigorous than modern intellect, but it took the wrong path.

2. The evidence of facts in mental inves. tigations is internal and cogitative, whilst in those which are physical it is external and experimental illustrated by chemical experiments, giving evidence of the facts that there is fire in water, and that in a clear saline solution (Epsom salts) there exists an insoluble material-illustrated by the mathematical theorem, that the square of the hypotenuse of a right-angled triangle, is equal, &c.

It was in this part of his subject for no where else had it any bearing on physical phenomena that the lecturer appeared to think, that by adducing such obvious dif ferences in the form of investigation, as are denoted by the terms, experiment and cogitation, he was pointing out "distinctions" in the nature of investigation. The form is determined by the purport or the peculiar subject of inquiry, and may be experimental or cogitative, or both, either in mental or physical science, but the process of investigation, in itself, is purely a mental procedure, whichever the form, or whichever the science, and to it belong such mental distinctions only, as are indicated by the terms deduction and induction. Indeed to speak still more correctly, experiment, like observation, is one of the conditions of investigation, rather than one of its forms, but cogitation is essential to it, as being the plastic spirit which uses the materials that the other, as the instrument, obtains, and moulds and fashions them into coherent forms. In the order or method of this mental proceeding, two "leading distinctions' may be observed, according to which the "investigation of phenomena' may be characterised as either deductive or inductive. To have had those distinctions pointed out, and the advantages of their corresponding methods elucidated, as being equally subservient in mental as in material philosophy, would indeed have been a treat.

In his observations on the uncertainty of the evidence afforded through the medium of the senses, the lecturer quoted Lord Brougham in support of his own opinion, that we are not so clearly cognizant of the

existence of matter as of mind, and illustrated the deceptive nature of sensible evidence, by the exhibition of specimens of machine medallion engraving, which conveys the illusive idea of relief, and of a specimen on a large scale of the philosophical toy, the invention we believe of Dr. Roget, which conveys to the eye the impression of a whole and perfect image, although depicted in moieties on the opposite sides of a revolving tablet. The lecturer, in conclusion, alluding to the vast difference which exists in different individuals in respect to their mental faculties, instanced the cases of Shakespeare and Newton, and eulogised them in glowing terms.

NOTES AND NOTICES.

Stephenson Memorial.-We observe, with pleasure, that a well-deserved tribute of admiration and respect is about to be paid to an individual, to whose genius and untiring energy, his country is deeply indebted for one of her grandest modern improvements-the formation of railways, and the application of locomotive power-we allude, of course, to George Stephenson, Esq. A committee has been formed, embracing many of the first names connected with the iron trade, to consider the subject of a "Stephenson Memorial," and we hear that a colossal statue is spoken of, to be erected in such part of the kingdom as may hereafter be determined upon, and formed of that most appropriate material-cast-iron.—Mining Journal.

The Iron Sailing Ship.-The first sailing vessel ever built of iron was, it will be recollected, constructed in Liverpool, and was, very appropriately named the Ironsides. She sailed for Pernambuco, which she reached after a passage of forty-seven days. Much interest, indeed, anxiety was felt to know whether the iron would influence the needle. We are happy to state, that the compass was correct, throughout the whole passage; and that, therefore, no fear need be entertained as to its general correctness on board of iron-built ocean-going vessels. The Ironsides may be shortly expected on her return passage.

Roberts's Self-acting Mule.-The petition of Mr. Roberts, of the firm of Sharp, Roberts, & Co., of Manchester, praying for a prolongation for seven years, of the several patents granted to him in the year 1825, for the United Kingdom of Great Britain and Ireland, for that important invention, was heard lately before the judicial committee of her Majesty's privy council:-present, the Marquis of Lansdowne, lord president; Lord Lyndhurst, Lord Brougham, and Sir Herbert Jenner.Counsel for the petitioner, Sir Frederick Pollock and Mr. Teed. No caveat having been entered to oppose the application, the Attorney-General briefly addressed their lordships, stating that on the part of the crown he had no objection to offer to the prayer of the petitioner being granted. A model of the machine was then exhibited, and the nature and objects of the invention were explained to their lordships. Evidence was next given in support of the allegations contained in the petition; and after a short consultation, the Marquis of Lansdowne, on behalf of the judicial committee, granted a prolongation of the several patents for the term prayed for, on account of the great ingenuity

and merit of the invention, and the obstacles which had from time to time been opposed to prevent the patentee from deriving a fair remuneration for so important an invention during the original term of the patents.

New Patterns and Inventions Bills.-We have received copies of Messrs. Mackinnon and Baines' "Bill for the better encouragement of arts and manufactures, and securing to individuals the benefit of their inventions for a limited time;" and Messrs. Thomson and Labouchere's "Bill to secure to proprietors of design for articles of manufacture, the copyright of such designs for a limited time." The former bills is similar to Mr. Mackinnon's of last year; the subject of fourteen years patents, we grieve to see, remains unattended to. We shall offer a few remarks on the subject in our next.

Beale's Patent Air Light.-Modes of obtaining artificial light seem now to be the scientific mania of the day. We have almost every week occasion to notice some new luminary with greater or less pretensions to superiority and economy. Mr. Beale some years ago patented a method of burning coal tar and other cheap oleaginous substances, by forcing a current of air through the burner at about the point of combustion; but in consequence of the unpleasant smell which the tar or other cheap oil produced, its use was confined to manufactories and places where this was defect of little consequence. Mr. Beale, some time ago, at the instigation of Mr. De Mourier, entered deeper into the theory of his invention, and has succeeded in so improving his apparatus as to render it capable of burning oil of various kinds, or rather generating gas therefrom and burning it mixed with a stream of atmospheric air, obtaining a most clear and beautiful light, and without smell or smoke. We have seen five lamps in action at Mr. De Mourier's private offices in Lombard-street, in which the merits of the invention are clearly evidenced. The stream of air is supplied to the lamps by means of a double bellows, similar to the bellows of an organ, kept in motion by a weight. Instead of the weight a spring may be used. There are, of course, numerous ways of supplying the air, but the method just described appears well adapted for private and public buildings. The proprietors of the patent, we understand, intend to contract to supply parties at half the price of gas. As we intend shortly to publish a detailed description of the whole apparatus, we shall not therefore now enter more particularly into its construction.

New Dibbling Machine.-Mr. James Hitchins, of this city, is about to introduce to the notice of the farmer and the public, a machine for dibbling wheat, turnips, or any kind of grain and seed. By a simple arrangement, seed and bone-dust, in small or large portions, are deposited together in holes made at exact intervals. The whole apparatus can be worked at the full speed of a horse in a walking pace. It is well known that bone-dust in drillrows is of small value except in the first stage of vegetation, and when not in actual contact with the seed, it is rather detrimental than beneficial. By this dibbling machine, 75 per cent. will be saved in the amount of bone-dust required, and nearly all the expense of thinning the plant and keeping them clean in future, will be economised.-Lincoln Gazette.

Salt Manufactory.-Manufactories are about to be established in various parts of the agricultural districts, for the purpose of supplying the farmers with marine salt, soda, and lime, for manure, at a reduced rate-and this is to be effected by establishing these works in such stations as are most easy of general access.-Mark-lane Express.

THE PATENT FRESH-AIR PNEUMATIC

GRATE.

Mr. Jeffreys's new warming and ventilating apparatus, "the fresh-air pneu. matic grate," is so named on account of the peculiarity in its structure, which causes the point of greatest pressure of the several currents of air entering the chimney to be on a vertical plane, instead of a horizontal one, as in common fire-places, where the pressure is in the chimney throat.

It has been the desire of all judicious improvers of grates and fire-places to bring the grate as far forwards as possible; but so long as the ascent of the smoke is in the usual course this can only be effected by lowering the front or breast-work. If the fire is brought

quite out of the chimney the front has to be closed down to, or near to, the upper bar, forming almost a close stove. If such a fire has the bars exposed the consumption of fuel is very large, and its warming power is small. There is a great rush of air through the fire, burning away the fuel, and the upper surface being shut in its heating influence is lost. Such a fire, though preferable to a close stove, is less cheerful than a common fire. In some particular cases an open fire can be set out in front of a chimney, as in some places in the north, but then a very large draught of air is required to force the current of smoke backwards into the hole leading to the chimney, and puffs of smoke are at all times liable to escape into the room.

The elevating of the front or breastwork of a fire-place so much improves its appearance and effect, that many persons are ready to sacrifice the advantage of a forward position of the grate, in order to command it. By putting the grate far in, as was common in former days, a very lofty and stately appearance may be given to the open front, but then the warming effect is lessened.

The grate we have now to describe commands both the advantages in their fullest degree. It is more open in front than any other grate, and is, nevertheless, so well set out, that a person quite in the chimney corner, has the fire right before him. It radiates as directly on both sides as it does forwards. Its range of radiation is in fact doubled.

Upon first seeing it the impression of most persons is that such a fire must