118 ARRANGEMENT OF APPARATUS. 



tening the plates in position, great care must be 

 taken to avoid touching them with the fingers, as 

 should this happen and indelible stain will make its 

 appearance at that spot during the subsequent de- 

 velopment. Having fastened the plates in position, 

 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 apparatus 

 are arranged. 



The right hand side of the cloth hanging over the 

 apparatus is then 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 miaro- 

 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 centring 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- 

 posed plate next the person in the breast pocket of 

 the coat ; every precaution being taken as before, to 

 prevent displacement. 



