141' 



UNDULATORY FORCES. LIGHT PHOTOGRAPHY. [PHOTOGRAPHIC AFTARATOT. 



ppoanuioea are tho same lu in the object which ha* been 

 copi.-d. Fitf. 142 represent* a negative, and Fig. 143 a 

 positive, of the same object 



Mr. m. i t- 



A positive picture may easily bo obtained by placing a 

 negative, face downwards, on another piece of prepared 

 paper, and proceeding as before. The light will thus pass 

 through the unchanged portions of the negative, and so 

 produce a darkening of the paper beneath it ; whilst the 

 dark portions of the negative, of course, prevent any 

 change in that part of the paper beneath them. The 

 positive, thus obtained, may be fixed by tho process 

 previously described. 



We have purposely restricted these experiments to 

 the simplest form of photographic practice. The materials 

 are easily obtained ; and if the process be repeatedly per- 

 formed, the student will gradually acquire an expert i 

 and, at the same time, meet with difficulties which he 

 may easily overcome. If, for instance, he observe brown 

 marks on the picture, he may guess that his fingers have 

 been their cause. White, round spots indicate p. 

 whore neither the salt or silver solution have touched the 

 surface of the paper, owing to the presence of air- 

 bubbles. Blotches, and large patches on the surface, 

 show that the paper is not suitable for the purpose. 

 Tbis may easily be avoided by the purchase of an article 

 specially prepared for photography ; but we still rec< >m- 

 niend that the tyro should begin in the simplest manner, 

 and so arrive, step by step, at success, by becoming gra- 

 dually acquainted with obstacles as they accidentally 

 present themselves. 



To gave trouble, and to simplify our instructions in 

 these elementary attempts, it may perhaps be as well 

 that we give a recapitulation of the whole of the 

 process ; and also special directions for obtaining positive 

 copies from negative pictures. 



1. Salt one side of the paper, taking care that no air- 

 bubbles are left between its surface and the liquid. 



2. Mark the salted side. 



3. Dry the paper. 



4. Render the salted side of the paper sensitive by 

 plai.-iiig that surface in the silver solution for about ten 

 minutes, taking precautions against the presence of air- 

 Imliblos, by drawing the paper over the solution whilst 

 holding it at one corner. This must be done by caudle- 

 light 



6. Dry the paper in a dark place, and, when dry, 

 keop it out of the light. 



C. To obtain a negative picture, place tho object on 

 the sensitive surface of the paper, and press thereon a 

 piece of plate-glass, so that the object and paper may be 

 in the closest possible contact 



7. Expose to day or sun light so long that the paper 

 may acquire a dark mulberry tint in those places where 

 the light has free access. 



8. When tho picture is finished, remove it into a dark 

 oom, and fix by means of a solution of hyposulphite of 



odtat' 



'.>. Wash abundantly in cold water, so as to remove all 

 trace of the salts. This should be done by placing the 



picture in a basin of water for some hours, and mean- 

 while frequently moving it in the liquid. 



10. The picture may then bo dried, and pasted or 

 * gummed on a piece of cardboard. 



11. To obtain a positive picture 

 from a negative, place the negative, 

 face downwards, on a piece of sensitive 

 paper, the two being pressed together 

 i'\ means of plate-glass, or otherwise. 

 When the picture is finished, proceed 

 as recommended in Nos. 8, 9, and 10. 

 If resident in any of our large towns, 

 tho operator may purchase paper which 

 is ready salted, and also covered with 

 albumen. This only requires to be 

 excited by placing the albumeniscd .-Me 

 on the silver solution, as named in No. 

 4. This paper may be prepared by 

 dissolving fifty grains of salt or sal- 

 ammoniac in two ounces of water, to 

 which twice as much of the clear white 

 or albumen of an egg has been added. 

 The mixture must be well shaken to- 

 gether, and then strained through muslin. The paper 

 may then be laid on its surface after the manner before 

 recommended for the salting process. The albumen 

 gives a nice gloss to the picture, and so greatly improves 

 its appearance. 



We need scarcely state, that an ingenious person may 

 employ the above process to a vast variety of interesting 

 and amusing purposes. Leaves of trees, flowers, ferns, 

 engravings, lace patterns, and an immense number of 

 similar subjects, may thus be easily copied : indeed, we 

 know of no branch of scientific application so readily 

 acquired, and more varied or interesting in its pursuit. 



We may here mention, that the ordinary process of 

 marking linen by means of common ' ' marking-ink, " 

 and various modes of dyeing hair, are really but appli- 

 cations of photographic principles and practice. In most 

 of these cases, solutions of the nitrate of silver are 

 employed; and the results obtained are identical with 

 those we have named, except so far as the objects to 

 which they are applied are concerned. 



Having thus attempted to introduce the reader to 

 some of the most elementary instances of the practice of 

 photography, we now proceed to describe more intricate 

 processes, by means of which the highest class of effects 

 are obtained; and which will of course require greater 

 attention, care, and perseverance in their pursuit, than 

 those to which we have hitherto referred. 



PHOTOGRAPHIC APPARATUS AND 

 CHEMICALS, ETC. 



BEFORE proceeding to detail the various processes now 

 in use, we shall enter into a description of the apparatus 

 which will be required by the student, and also mention 

 tho different chemicals employed by photographers. 



The chief photographic instrument is the camera. 

 We described some forms of this instrument under the 

 head of Optical Instruments; but such are of far too 

 incomplete a kind to be employed for photographic 

 purposes, in which the utmost accuracy of construction 

 hitherto attained has yet left many defects to be over- 

 come. We shall therefore endeavour to point out, not 

 only the best form of the instrument for various pur- 

 poses, but also shall suggest contrivances which may 

 assist the beginner in many circumstances in which he 

 may lie placed. 



A camera of an ordinary kind, suitable for a beginner, 

 may bo procured for a moderate sum ; but where the 

 means of the student will permit, none but the best 

 kind, as to construction and character of tho lei 

 should be employed. Many persons oommenoilig the 

 practice of photography, are content to do so with a:i 

 inferior instrument. Having thus to contend with ditti- 

 culties which, from their want of knowledge- of tlm 

 science of optics, they can neither overcome nor control, 

 they often entirely fail in obtaining good results, and, 



