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"History and Practice of Photogenic Drawing on the true Principles of the Daguerréotype." (Smith, Elder, and Co., Cornhill.) The contents are classified in four chapters. The first comprises the Bill for rewarding the inventors, granting to M. Daguerre an annual pension for life of 6,000 francs, (250l. sterling); to M. Niepce, jun., a similar pension of 4,000 francs, (166l. 13s. 4d.); these pensions being one-half in reversion to the widows of the inventors. Next is the bill presented by the Minister of the Interior, M. Duchâtel, to the Chamber of Deputies, in June last, proposing the above grants, explaining the partnership of MM. Daguerre and Niepce, and bearing M. Arago's guarantee for accuracy. The commission appointed to examine the discovery were the following members of the Chamber, MM. Arago, Etienne, Carl, Vatout, de Beaumont, Tournouer, Delessert (François), Combarel de Leyval, and Vitet, all names distinguished in science. The special commission of Peers was composed of Barons Athalin, Besson, Gay-Lussac, the Marquis de Laplace, Vicomte Siméon, Baron Thénard, and the Comte de Noé. The next documents are Arago's very minute and interesting Report to the Deputies, and a similar Report from the Special Commission to the Peers.

Chapter II. includes the practical and historical details of the invention; and relates the partnership of Niepce and Daguerre; with experiments and improvements. A proof of Daguerre's priority to Niepce is the application of iodine, which constitutes the great distinction between the processes of the two experimenters; "in a word," says the translator, "between the approximation and the real principle."

Chapter III. is, however, still more practical in its details, as a quotation will show:-The designs are executed upon thin plates of silver, plated on copper. Although the copper serves principally to support the silver foil, the combination of the two metals tends to the perfection of the effect. The silver must be the purest that can be procured. As to the copper, its thickness ought to be sufficient to maintain the perfect smoothness and flatness of the plate, so that the images may not be distorted by the warping of the tablet ; but unnecessary thickness beyond this is to be avoided, on account of the weight. The thickness of the two metals united ought not to exceed that of a stout card.

The process is divided into five operations:

1. The first consists in polishing and cleaning the plate, in order to prepare it for receiving the sensitive coating, upon which the light traces the design.

2. The second is to apply this coating.

3. The third is the placing the prepared plate properly in the camera obscura to the action of light, for the purpose of receiving the image of nature.

4. The fourth brings out this image, which at first is not visible on the plate being withdrawn from the camera obscura.

5. The fifth and last operation has for its object, to remove the sensitive coating on which the design is first impressed, because this coating would continue to be affected by the rays of light, a property which would necessarily and quickly destroy the picture.

The operations are then minutely described; under the third of which is illustrated the time necessary for producing a design, which depends entirely on the intensity of light on the objects, the imagery of which is to be re-produced. At Paris, for example, this varies from three to thirty minutes.

The several instructions are illustrated by six pages of outline diagrams of the requisite apparatus. Thus, Plate I. shows the wire frame for supporting the plate while heating; the "plate of plated silver" on which the design is made; the board upon which the plate is laid; the spirit-lamp, and the muslin bag, with pumice powder for polishing. Plate II. shows the box for iodine, used in the second operation; and a grooved case for preserving the plates from injury. Plate III. "represents four different positions of the frame into which the plate with its wooden tablet is put, on removal from the iodine process;" the objects being to adapt the plate to the camera obscura, and to protect the iodine coating from the action of light till the moment in which it receives the focal image. Plate IV. shows the camera obscura, as adapted to photogenic delineation. Plate V. represents three views of the apparatus for submitting the plate to the vapour of mercury; a kind of case, provided with a spirit-lamp, and a thermometer on one side to denote the rate of the process. Plate VI. shows various apparatus for the last operation of washing the plate as three troughs, with the plate placed therein; the funnel for filtering the saline wash; a little hook for shaking the plate while in the wash; and a wide-mouthed vessel for warming the distilled water. The fourth and last chapter elucidates another new art, invented by Daguerre-the principle and practical details of Dioramic Painting.

The recipe is briefly as follows:-A copper-plate plated with silver, its surface well cleansed with diluted nitric acid, is exposed to the action of the vapour of iodine: this forms the first coating, or ground; which is inconceivably thin, and requires to be perfectly even. The plate thus prepared is placed on the table of the camera obscura; and after remaining eight or ten minutes, according as the subject or the degree of light may require, is withdrawn. At this stage of the process, however, the most practised eye will not discern the slightest trace of the action of the light on the prepared surface. The plate is then exposed, in a proper apparatus, to the vapour of mercury; and, when heated to sixty degrees, the picture appears as if by magic. A singular, and hitherto inexplicable circumstance, requires to be noticed in reference to this part of the process; viz., that the plate must be in an inclined position; and that, if it be placed directly opposite the aperture whence the vapour of the mercury escapes, the result will not be satisfactory. Lastly, the plate must be dipped in hyposulphate of soda, and afterwards well sluiced with distilled water: the operation is then complete.

The first experiment made in this country with the Daguerréotype, was exhibited by M. St. Croix in London, on the 13th of September. The place of exhibition was No. 7, Piccadilly, nearly opposite the southern crescent of Regent-street; and the picture produced was a beautiful miniature representation of the houses, pathway, sky, &c., resembling an exquisite mezzotint.

In the Philosophical Magazine, November, Mr. Towson explains an important fact which had hitherto escaped observation. It appears that M. Daguerre does not use an achromatic lens; and that the focus he employs is obtained by advancing or withdrawing the frame of the obscured glass, until he obtains the outlines of the subjects with the greatest neatness. This method would be most correct, if the chemical rays were identical with the luminous rays. If such were the case, the effect produced on this plate would be precisely that which had appeared on his obscured glass. But, it is a well known fact, that the chemical rays are more susceptible of refraction than the luminous rays; wherefore, in order to obtain the neatest effect, it is indispensable that the camera should be adjusted to the focus of the chemical rays. The author then details his improved method, by which the time of exposing the plates in the camera may be reduced from three or five minutes to ten or twelve seconds. The use of larger lenses, which the correction of the focus enables him to adopt, would, he considers, render the Daguerréotype applicable to taking portraits from life; allowed to be a great desideratum, in the discussion at the Institute, after M. Arago had announced Daguerre's process.

Dr. Donné is stated to have applied, with success, the ordinary process of engraving directly to the proofs taken with the Daguerréotype; a discovery almost as important as the invention of the apparatus itself.

For preserving the impressions of the Daguerréotype, M. Dumas has found to succeed, better than any other composition, a varnish (one part dextrine to five of water) applied hot to the plate. The photogenic impression will be thus free from any danger of friction, and may be copied by means of transparent paper, &c. M. Sylvester has employed a composition of dextrine, two parts; water, six parts; and alcohol, one part: but, both compositions interfere with the brilliancy of the plate.

M. Arago has since stated that instead of placing the iodine in the box with the plate, the latter is first impregnated with the vapour, and this is placed in a flat box, within half an inch of the plate on which the drawing is to be taken. The box is then to be shut, and in two minutes the silver plate will have acquired the proper tint.

Dr. Schafhentl, of Munich, has exhibited a new process of producing photogenic drawings combining Daguerre's minuteness with the light and shadow of an original drawing, by means of Indian ink. The preparation of these new photogenic plates is, however, as yet too complicated for popular practice.

*** Among the more popular as well as important papers on the New Art, are letters from Mr. Bauer, F.R.S., and M. Niepce, on the originality of the invention; reported in the Literary Gazette, 1839, p. 137: also, an elaborate paper by Mr. A. Smee, at p. 314 of the same journal. A cheap and simple method of preparing papers for photogenic drawings, in which the use of any salt of silver is dispensed with, has been communicated to the Society of Arts for Scotland, by Mr. Mungo Ponton, F.R.S.L., and is reprinted in the Literary World, Vol. i. p. 254. In the Reports of the Proceedings of the British Association will be found many important observations by Mr. H. F. Talbot, and Sir John Herschel; the latter describing a remarkable property in the extreme red rays of the prismatic spectrum, which had occurred to him in his experiments on Mr. Talbot's photogenic paper. The Athenæum for the year

contains, in addition to the reports of papers read to Societies, experiments and new preparations, by correspondents; too numerous to particularize. In Jameson's Journal, Vol. xxvii., will be found notes by Sir John Robinson, p. 155; and observations by Dr. Fyfe, p. 144. In the Philosophical Magazine, Vol. xiv., p. 196, will be found Mr. H. Talbot's "Account," extending through fifteen pages; at p. 365, of the same volume is a "Note" communicated to the Royal Society by Sir John Herschel and at p. 475, are extracts from the proceedings of the Royal Irish Academy, proposing the light of incandescent coke to blacken photogenic paper, as a substitute for solar light. or that from the oxy-hydrogen blow-pipe with lime. And in the Philosophical Magazine, Vol. xv., p. 381, will be found Mr. Towson's paper on the proper focus for the Daguerreotype, above quoted. An article on the application of the art to botanical purposes by Dr. Golding Bird, appears in the Magazine of Natural History, April, 1839. In the Mechanics' Magazine, Vol. xxx., p. 329455, are letters from Sir Anthony Carlisle, and Mr. T. Oxley; at p. 428, a letter from Mr. Egerton Smith; and an Abstract of Daguerre's Treatise, p. 465 -471, &c.

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OPERATION OF POISONS.

On June 13, was read before the Royal Society," a Series of Experimental Researches on the mode of operation of Poisons," by J. Blake, Esq. In this paper, the author examines more particularly the action of those poisons which appear to produce death by affecting the nervous system. After reviewing the evidence adduced in support of the opinion that the effects of some poisons are owing to an impression made on the nerves of the part to which they are directly applied, he proceeds to relate a series of experiments undertaken in order to show with what rapidity the blood is circulated through the body, and tending to prove that a substance may be generally diffused through the system in nine seconds after its introduction into the veins. Experiments are then related in which the more rapidly fatal poisons had been used, and in which it was found that an interval of more than nine seconds always elapsed between the administration of a poison and the appearance of the first systems of its action. The mere contact of a poison with a large surface of the body appears to be insufficient to give rise to general effects, as long as it is prevented from entering into the general circulation. Various causes of fallacy in experiments of a similar kind, which have been adduced in support of an opposite opinion, are pointed out. The following is a summary of the conclusions arrived at by the author:

1. The time required for a substance to penetrate the capillary vessels may be considered as inappreciable.

2. The interval elapsing between the absorption of a substance by the capillaries, and its general diffusion through the body, may not exceed nine seconds.

3. An interval of more than nine seconds always elapses between the introduction of a poison into the capillaries, or veins, and the appearance of its first effects.

4. If a poison be introduced into a part of the vascular system nearer the nervous centres, its effects are produced more rapidly.

5. The contact of a poison with a large surface of the body is not sufficient to give rise to general symptoms, as long as its diffusion through the body is prevented.-Athenæum.

126

Electrical Science.

VOLTAIC COMBINATIONS,

ON May 30, was read to the Royal Society, the "Fifth letter on Voltaic Combinations; with some account of the effects of a large Constant Battery;" by J. F. Daniell, Esq. The author, pursuing the train of reasoning detailed in his preceding letters, enters into the farther investigation of the variable conditions in a voltaic combination on which its efficiency depends: and the determination of the proper proportions of its elements for the economical application of its power to useful purposes. He finds that the action of the battery is by no means proportioned to the surfaces of the conducting hemispheres, but approximates to the simple ratio of their diameters; and hence concludes that the circulating force of both simple and compound voltaic circuits increases with the surface of the conducting plates surrounding the active centres. On these principles, he constructed a constant battery consisting of seventy cells in a single series, which gave, between charcoal points, separated to a distance of three-quarters of an inch, a flame of considerable volume, forming a continuous arch, and emitting radiant heat and light of the greatest intensity. The latter, indeed, proved highly injurious to the eyes of the spectators, in which, although they were protected by grey glasses of double thickness, a state of very active inflammation was induced. The whole of the face of the author became scorched and inflamed, as if it had been exposed for many hours to a bright midsummer sun. The rays, when reflected from an imperfect parabolic metallic mirror in a lantern, and collected into a focus by a glass lens, readily burned a hole in a paper at a distance of many feet from their source. The heat was quite intolerable to the hand held near the lantern. Paper steeped in nitrate of silver, and afterwards dried, was speedily turned brown by this light: and, when a piece of fine wire-gauze was held before it, the pattern of the latter appeared in white lines, corresponding to the parts which it protected. The phenomenon of the transfer of the charcoal from one electrode to the other first observed by Dr. Hare, was abundantly apparent; taking place from the zincode (or positive pole) to the platinode (or negative pole). The arch of flame between the electrodes was attracted or repelled by the poles of a magnet, according as the one or the other pole was held above or below it; and the repulsion was at times so great as to extinguish the flame. When the flame was drawn from the pole of the magnet itself, included in the circuit, it rotated in a beautiful manner. The heating power of this battery was so great as to fuse, with the utmost readiness, a bar of platinum, one-eighth of an inch square: and the most infusible metals, such as pure rhodium, iridium, titanium, the native alloy of iridium and osmium, and the native ore of platinum, placed in a

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