ARBANGEMEKT OF APPARATUS, ETC. 107 



is laid with its back on the velvet side of the second 

 zinc partition, its gelatinised surface then looks to- 

 wards us. Whatever plan is now adopted for fas- 

 tening the plates in position, great care must be 

 taken to avoid touching them with the fingers, dur- 

 ing the process; as should this happen an indelible 

 stain will make its appearance at that spot during 

 the subsequent development. Having fastened 

 them we shut up the dark slide or plate carrier, 

 and enveloping it in a dark cloth, or better placing 

 it in the inside breast pocket of our coat, we carry- 

 it to the apartment where the microscope and ap- 

 paratus are arranged. 



The right hand side of the cloth hanging over the 

 apparatus is slightly raised, the dark slide slipped 

 quietly and carefully underneath it, and substituted 

 for the ground glass of the camera. 



The sliding door covering the plate next the micro- 

 scope is then drawn out, and a delay of a few seconds- 

 made to allow all vibration to cease. 



The utmost care is required for these manipula- 

 tions, and if the dark slide and camera are not ac- 

 curately made, some sticking or jarring very likely 

 to cause displacement and endanger the centering 

 of the apparatus is certain to occur. 



During this interval a watch is placed on the stand 

 near the lamp where the time can be easily observed. 

 The opaque card is now gently removed, the re- 

 quisite exposure, say ten seconds given, and the card 

 gently replaced ; the dark slide shut, the carrier re- 

 moved from the camera, and placed with the ex- 



