NOTES AND MEMORANDA. 63 



photographic camera, which in one way or another had to be connected 

 with the tube of the microscope, but also a small photographic atelier 

 with a dark chamber. It required a certain time to learn how to 

 prepare the plates, and many thought that they could only acquire 

 skill in working from a course taken under a practical photographer. 



The important advances in general photography have now been 

 extended to the application of it to microscopical research, and 

 endeavours have been made for some time to discover a process which 

 will obviate the inconvenience of a photographic dark chamber and 

 of having to prepare the plates each time, and which will allow of the 

 sensitive plates being kept in stock, so that their complete sensitive- 

 ness is preserved for an indefinite time. 



Of late years, the most various methods of preparing photographic 

 dry plates have been proposed. The best, most tested, and surest 

 process, however, is that of F. Wilde, of Gorlitz, who has recently 

 tested most carefully various approved forms of the dry process, and 

 so improved it that anyone by keeping closely to the directions given 

 with the plates, which can be obtained ready prepared, is in a position 

 to produce excellent photographic pictures. A dozen prei^ared plates, 

 each containing from 70 to 80 square centimetres of surface, cost 

 tix to seven shillings. 



I * have occupied myself now for nearly twenty years in my leisure 

 moments with the apj)lication of photography to subjects of natural 

 history, either generally, or specially in microscopic work, and 

 possess the requisite facility in all photographic manipulations. In 

 spite of this, however, since I have become acquainted with Wilde's 

 dry plates I have laid aside every other contrivance, and work only 

 with that process. No method others the same certainty, entails so 

 little loss of time, and allows of such simple working, and I can there- 

 fore recommend it in the most pressing manner to my collaborators. 



For the benefit of those who might wish to prepare the jilates 

 themselves, it may be stated that the sensitive covering consists of an 

 emulsion of collodion, in which various salts of silver, chiefly 

 bromide of silver, are suspended. Glass plates upon which a solution 

 of 1 gramme of caoutchouc in 150 to 200 grammes of benzine has 

 been poured, are covered with this emulsion, which, every time it is 

 used, must be well shaken, and then allowed to rest again for some 

 minutes. When the film has set a little the plates must be forthwith 

 dried by the application of moderate heat, which may be done either 

 in a small drying oven, or by moving them to and fro over a plate 

 beneath which a spirit lamp is placed; after being dried, the plate 

 is ready for use, either at once or at any subsequent time. 



To use the plates all that is necessary is a conical tube for the end 

 of the microscope, such as I have fully described in my work on 

 ' Light as Employed in Scientific Research,' page Slo, the wide end 

 of which is placed uppermost. Connected with the tube is a cross 

 piece on which the photograjihic cassette and the ground glass are 

 placed. Such an apparatus, which can be got complete for about 

 20s., is quite sufficient to obtain the most beautiful micro-photographs 

 * Dr. S. Th. Stein, in ' Zeitschrift fiir Mikioskopie,' vol. i. p. 140. 



