PHOTOGRAPHY. 



distance of two-thirds of its diameter ; in the case 

 of a combination, it is placed between the lenses. 

 The advantages of its use have been already 

 stated ; the disadvantage is manifestly loss of 

 light, and a consequent increase of time required 

 in exposure. 



III. Camera-stand. These are made of various 

 forms the most common and most portable, as 

 well as most convenient for general purposes, is 

 the tripod. It consists of three light but tough 

 legs, steadily hinged upon a small table of wood 

 or triangle of metal. A screw passes through the 

 centre of this table, or through a bar of metal fixed 

 between two sides of the triangle, and corresponds 

 with a female screw inserted into the bottom board 

 of the camera, so that the stand and camera can 

 be firmly bound together. 



The various processes by which photographic 

 pictures may be obtained now claim our atten- 

 tion. We can enter fully into those only which 

 are at the present time in greatest repute among 

 operators ; it will suffice to give a general idea of 

 the nature of the others, as it would be beyond the 

 limits of this article to dwell upon them all in 

 detail. In historical order, since the discovery of 

 the art, they stand as follows : Daguerreotype, 

 Calotype or Talbotype, Wax-paper, Albumen on 

 Glass, Collodion. All these have, since their first 

 introduction, undergone modifications more or less 

 extensive ; and the variety of formulae proposed, 

 shews that considerable latitude in practice may 

 be allowed. 



DAGUERREOTYPE. 



This process derives its name from M. Daguerre, 

 its discoverer, and is essentially distinct in some 

 of its features from all others. The pictures it 

 gives are, when viewed in most lights, positive or 

 direct, as given in the camera, though they also 

 appear as negative when seen at certain angles. 

 Its results are very beautiful, but as it has been 

 altogether superseded, our description of it shall 

 therefore be brief. The plates upon which the 

 pictures are produced consist of copper, thinly 

 coated on one side with silver. The plate is first 

 subjected to the action of vapour of iodine, and then 

 to the vapour of bromine, and is now ready for 

 placing in the camera, where a short exposure is 

 sufficient. To develop the image, the plate is 

 exposed to the vapour of mercury, which attaches 

 itself to those parts which have been acted on by 

 the light. When fully developed, the picture is 

 fixed by immersion in a solution of the salt called 

 hyposulphite of soda. 



CALOTYPE OR TALBOTYPE. 



The first of these names is derived from the 

 Greek *xf, ' beautiful,' and means ' beautiful 

 picture ; ' the second is from that of the discoverer, 

 Mr Fox Talbot. He first communicated it to the 

 Royal Society in 1839, and, under a more perfect 

 form, patented it in 1841. This may be said to 

 have been the starting-point of British photog- 

 raphy, as the discovery of Daguerre had so short 

 time before been upon the continent. The pic- 

 tures obtained by this method are upon paper, 

 and depend upon the peculiar action of light 

 on the iodide of silver. Paper having been 

 coated with the iodide referred to, and pres- 



ently to be described, and being thus made 

 sensitive to light, is placed so as to receive the 

 camera image : and according to the varied 

 brightness of the light in the parts of the image, 

 there is induced a tendency to blacken in corre- 

 sponding degrees of intensity on the subsequent 

 application of what is called a developing agent ; 

 so that, where there is a shadow in nature, there 

 will be little or no action, and the paper will 

 remain white, or nearly so ; and vice versd. The 

 picture is thus the reverse of nature ; in other 

 words, it is what we formerly defined as a 

 negative. This, instead of being a defect, is of 

 the highest importance, since it permits a system 

 of transfer by superposition, by which copies 

 called, in contradistinction, positives may be 

 obtained to an unlimited extent. The pictures 

 produced by this process are very artistic and 

 bold in effect, and give fine results for some kinds 

 of landscape and architectural objects ; and 

 although excellent results may be obtained in por- 

 traiture as, for example, those produced by the 

 late Mr R. Adamson and Mr D. O. Hill of Edin- 

 burgh yet the amount of light which is necessary 

 to produce the required change is too great to 

 render it very applicable for this purpose. The 

 texture of the paper also interferes sadly with the 

 delicacy which is desirable in portraits, and con- 

 sequently the process has been almost entirely 

 abandoned. The following description will, how- 

 ever, enable the amateur to practise it success- 

 fully. 



Having procured a suitable paper that known 

 among photographers as Papier Saxe answers well 

 cut it in pieces of about a quarter of an inch less 

 each way than the camera-slide to be used. They 

 are next to be iodised that is, coated on one side 

 with iodide of silver. This is done as follows : 



Take of nitrate of silver 50 grains, and dissolve 

 it in 2 ounces of distilled water ; add 7 drachms 

 of iodide of potassium, and shake the mixture 

 until the yellow iodide of silver, which is at first 

 precipitated, is nearly re-dissolved. The solution 

 should not become quite clear; should it do so, 

 two or three drops of water must be added till the 

 turbidity is slightly restored ; allow this to subside, 

 or filter the solution through dry bibulous paper. 

 The sheet of paper to be used is now laid flat 

 upon a board which is covered with a piece of 

 blotting-paper, and this iodising solution is copi- 

 ously, but without pressure, applied to the best 

 and smoothest side of it by means of a pellet of 

 cotton-wool fastened to a handle, or by a good 

 camel-hair brush. The sheet must now be allowed 

 to drain, and then rapidly dried, collecting the 

 drippings in some suitable vessel Each sheet is 

 to be so treated in succession. They are then 

 placed one by one in a large basin of pure tepid 

 not hot water, where they will assume on the 

 coated side a primrose-yellow colour. The water 

 is changed after five minutes, and again three 

 times during six hours. The sheets are now 

 pinned up by one corner, and allowed to dry 

 spontaneously. In this state they are iodised, 

 and will keep good for a long time. They are 

 insensitive to light, and indeed it has been found 

 that exposure to sunlight for a short time before 

 use has a beneficial effect 



To render this paper sensitive for the purpose 

 of obtaining pictures, it must be treated as fol- 

 lows : Having laid a sheet flat over blotting-paper, 



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