ARRANGEMENT OF APPARATUS. 127 



kept on the object, as frequently a slight alteration 

 of the distance of the perforated disc from the glass 

 slip, especially when the light is too great, produces 

 the desired effect. With regard to the proper dis- 

 tance of the condenser from the object; we have 

 found double its focal length, with the bull's eye one 

 inch from the lamp flame, the most favourable posi- 

 tion as a rule. Much, however, depends on the 

 thickness of the glass slip, on which the object is 

 mounted. Some recommend the image of the lamp 

 focussed on the object, this practice is only men- 

 tioned to be condemned. 



Having once found the proper distance for a con- 

 denser with any particular object, the number of 

 divisions marked on the tube of the substage appar- 

 atus, if entered in our note book, enables us to re- 

 peat it ad infinitum. 



When the proper quantity, and intensity, of illu- 

 mination is obtained, we proceed to place the camera 

 in position, observing the precautions mentioned 

 when describing a similar process with the one inch. 



The actinic focus is found in the same way, and 

 the camera being covered with a dark cloth, the 

 sulphate of copper cell is clamped in position. 



The light is sufficiently intense for the wet plate 

 process. We therefore proceed to the dark room, 

 and sensitise a plate according to the instructions 

 contained in a previous chapter, drain it as quickly 

 and thoroughly as possible, and place it face down- 

 ward in the dark slide used for that purpose. 



If it was necessary to caution the amateur against 

 touching the sensitised surface with his fingers in the 



