ARRANGEMENT OF APPARATUS. 137 



The sixteenth immersion being employed, the dry 

 front of the eight will be found to answer admirably 

 when used as in last process. 



All subsequent operations are conducted in exactly 

 the same manner. 



Dry plates or the wet process may be used, the 

 former is ten times as rapid as collodion requiring an 

 exposure of from one to five seconds. No fixed rule 

 can be given for exposure with sun-light for the rea- 

 sons already mentioned. 



Our readers are cautioned against expecting suc- 

 cess at the first trial, unless they have had some 

 previous experience in photography. On this ac- 

 count the production of negatives with an ordinary 

 camera and lens is recommended before attempt- 

 ing photo-micrography. 



When carrying out the methods here described, 

 avoid speaking or walking in the same or adjoining 

 apartment during exposure as this is very likely to 

 cause vibration of the instruments. 



Too great care cannot be taken to prevent the 

 entrance of actinic light. All instruments must be 

 lined with black velvet; or perhaps better, painted 

 inside with a very thick mixture of lamp black in 

 thin glue. When in position the microscope and 

 camera should be covered with a dark cloth be- 

 fore the substitution of the plate carrier for the 

 ground glass and subsequent exposure. Every means 

 must be adopted to prevent the entrance of actinic 



