OF MICROSCOPIC OBJECTS. 205- 



citric acid solution, with the addition of a little alcohol. 

 The fixing may be effected by a strong solution of hypo- 

 sulphite of soda, and the picture should then be very well 

 washed with pure water. When dry, the photograph must 

 be mounted with Canada balsam, in the same manner as 

 any ordinary object ; but great heat must not be used, or 

 the picture may be injured. 



When ordinary daylight is employed for this purpose, a 

 dark slide will be required for the prepared plate, in the 

 same way as for photographing landscapes, &c. These 

 dark slides are generally made by each individual to suit 

 his particular arrangements of negatives; but it may 

 be here recommended that the operator should always 

 focus, in the same slide which he is about to use, as so 

 small a difference in distance lies betwixt perfection and 

 failure. 



For an ordinary student, perhaps the preceding method is 

 that which is the most readily used, and consequently the 

 most generally available ; but almost every one has a dif- 

 ferent arrangement of microscope, by which he procures 

 these minute pictures. Mr. Shadbolt (one of our most 

 successful photographers) gives the following instructions : 

 "Having removed the upper stage-plate of a large com- 

 pound microscope, I replace it with one of wood, supplied 

 with guide-pins of silver wire, in order to admit of its sup- 

 porting a slip of glass coated with collodion, and excited in 

 the nitrate of silver bath in the usual way. If the ordi- 

 nary brass stage-plate were left undisturbed, it is obvious 

 that it and the excited slip of glass would bo mutually 

 destructive. 



" The microscope is now to be placed in a horizontal 

 position, the objective, intended to produce the picture, 

 made to occupy the place usually filled by the achromatic 

 condenser on the sub-stage of the microscope, while another 

 objective is screwed into the lower end of the body of the 

 instrument, which is used not only to focus with, but also 

 to make the requisite allowance for actinic variation. 



