Class X.] CAMERAS; PHOTOGRAPHIC GLASS; IMPROVEMENTS IX PHOTOGRAPHY.
edges, placed at an angle of 45°, and designed for makingreversed copies of drawings on lithograghic stone or woodblocks. It may also be fitted with lenses for enlargingor reducing copies, and for sketching from nature uponthe stone. A Prize Medal was awarded to Messrs. Varleyand Son.
Abraham, Abraham, and Co. (No. 263, p. 436) exhibita portable sketching camera, furnished with a meniscusand prism in the place of a lens and mirror. Whendown, the size of the box is 15 inches in length, 8 iuwidth, and 3^ in depth.
Plagxiol (France , No. 1679, p. 1257). T*his is by farthe largest camera in the Exhibition; the picture-boardis 24 inches square, and the object lens is 8 in diameter,double and achromatic. The picture was clear anddistinct, as far as unfavourable circumstances wouldallow of the examination. It is furnished with a clearguard-tube in front of the object-glass, of 4 inches pro-jection, amply sufficient to cut off side light. The object-glasses are separated by 15 inches, or about double theiraperture. The clear space which all the object-glassillumines, scarcely exceeds 6J inches in the centre of thepicture; at the edges and corners the defalcation oflight is very great. This, however, seems to be unavoid-able.
Large as is this camera, it is very far from being thelargest that has been constructed. The use of greatcameras for copying photographic plates aud MSS., espe-cially tables, is becoming common in France . We haveheard of some cameras which give pictures nearly a metrein length. A Prize Medal was awarded to M. Plagniol.
Schiertz (France , No. 999, p. 1227) exhibits a camera,the object-glass of which is 2} inches in diameter. Thereis a stop, and the light is so effectually intercepted by thecell and. tube of the second object-glass, that the sides ofthe field are rendered obscure, and the top, bottom, andcomers very dark: not one-fifth of the central light iseffective. The plate for receiving the image is 9 by7 inches, and the focal distance from the hinder lensal>out 8 inches; the field is fiat, and the image clear andgood. The mahogany stand is good, but is not welladapted for taking panoramic views. A Prize Medal wasawarded to M. Schiertz.
Harrison (United States, No. 223, p, 1450) has ex-hibited two or three cameras, but as they are not mountedin boxes, aud consist only of the brass-work and lenses,there were no means of trying their performance. Theyare constructed on the usual principle of double achromaticobject-glasses, to give a flat field. The largest is about4 inches aperture.
Albert (Frankfort-on-Maine , No. 7, p. 1121) exhibitsa camera, with a double achromatic object-glass, 54 inchesclear aperture: there is a slight stop placed between thetwo glasses, hut it cuts off only the reflected light at thesides. The pictures produced are 14 by 11 inches; butthe area fully illuminated is only inches in diameter,and the corners are very dark. With the full aperturethe image in the centre of the field is somewhat imper-fect; it will not bear magnifying, aud sharp clear defini-tion cannot be attained. Honourable Mention was awardedto Mr. Albert.
Rougkt de i/Isle (France , No. 1455, p. 1245). Acamera-lucida for copying drawings, by reflection andvision at the same time, through a large vertically-placedsheet of plate glass. The drawing to be copied is laidhorizontally on one side of the glass, and the paper toreceive the copy on the other; the outlines are thentraced by hand with freedom and facility, there being nonecessity for using only one eye, or for fixing the positionof the head. It is the simplest form of the camera-lucida.It inverts right and left; but this may be obviated, insome cases, by a looking-glass. The adjustments areeasy and simple. Honourable Mention was awarded toM. Kouget de l’lsle.
Photographic Glass.
Messrs. Chance and Co. (Class XXIV., No. 22, pp. 700,701) have exhibited flint glass, in discs aud in plates,adapted for the construction of object-glasses for Daguer-reotjpe and Talbotype apparatus and cameras. Of these j
discs one is as large as 20 inches in diameter, and thereare some thin plates of the same kind of glass forcutting up.
The density of this glass is 3’20; the index of itsrefractive power is 1*60.
Huron (France, No. 443, p. 1199) has exhibited acollection of glasses of 6, 8, 10, and 12 inches diameter,for dissolving views.
Rapid as have been the discoveries connected withPhotography, aud great as are the improvements it has| received since the invention of M. Daguerre , there is yet; much to be done to enable it to rank amongst the sciences! of the age. It holds a place at present intermediatei between an art and a science, a position eminently favour-j able to development in either direction. Its pursuit, asi an elegant and most extensively useful art, affords a strongmotive for inquiry and experiment in the improvementof its processes; in the course of which, an infinity offacts, new aud unexpected, come forward, every one ofwhich may turn out to be the embodiment of some preg-nant scientific principle; nay, even the smallest minutiaeof manipulation on which it is found that success orfailure in the production of artistic effect depends, may,if duly observed and reasoned on, afford indications, link-ing together the known and the unknown in opticalscience, and tending to bring these mysterious operationsof light within the pale of exact reasoning. On the otherhand, science is too much in the habit of repaying to art,with interest, every assistance of that nature, to leaveroom for doubt of similar results in this instance, whenonce the principles of operative chemistry shall haveassumed a definite form and subjective connexion. It isthis which affords us full assurance that Photography isyet in its infancy, and that all which has been hithertoaccomplished—marvellous aud exquisite though it he,is as nothing to what will be performed when the veilshall be removed, which, for the present, obscures itstrue scientific principles. In this point of view thephotographic study of the prismatic spectrum per se,apart from all artistic combinations and coloured media,cannot be too strongly recommended to experimenters,and we lament to observe only one instance, in the wholeExhibition (that of M. Claudet) in which this studyappears to have been in any way followed up, so as toafford exhibitable results. Mr. Ross is understood, also,to construct the object-glasses of his photographic cameras,witli especial reference to the excessive development ofthe actinic spectrum beyond the luminous one, in thedirection of the violet rays. When bromine is used iuthe preparation of the plate or tablet, it may be questionedhow far this is really an improvement? Should meansbe discovered of truly representing the colours of objects,and limiting the action to the luminous ray, the con-ditions of achromaticity for the photographic camera willbe the same as for the telescope.
The fine collection of Photographs now exhibited willtend much to the advancement of this beautiful art, byshowing us what has been done, and also by indicatingthat which it is necessary yet to do; aud it w'ill doubtlessmark an era from which to date many improvements.
Since the epoch when M. Daguerre and Mr. Talbotfirst divulged their respective processes for impressingphotographic images on silver and on paper, scientificmen, both at home and abroad, have, by their increasingresearches and improvements, brought Photography to adegree of perfection, which, however short of what itmay one day acquire, yet seems incredible, consideringits brief existence. Perhaps its advance cannot be morestrongly proved than by the fact that the method, firstadopted but a few years since, for procuring daguerreotypeportraits, required that a person should sit without movingfor twenty-five minutes in a glaring sunshine. Theimprovement developed in the almost instantaneous pro-cess of the present day is most striking.
It is not the object of this report to trace the history ofinventions, nor to decide on claims of priority, especiallyin relation to a subject w'hich has received accessionsfrom such innumerable quarters, and called into action
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