OF MICROSCOPIC OBJECTS. 139 



soda, and the picture must 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 landscape, &c. These dark slides are generally 

 made by each individual to suit his particular arrangements of 

 negatives, &c. ; but it may be here recommended that the opera- 

 tor 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 above method is that which 

 is the most readily used, and consequently the most generally 

 available ; but almost every one has a different arrangement of 

 microscope, &c., 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 compound microscope, I replace it with one of wood, 

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

 supporting a slip of glass coated with collodion, and excited in the 

 ' nitrate of silver bath in the usual way. If the ordinary brass stage 

 plate were left undisturbed, it is obvious that it and the excited 

 slip of glass would be 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. 



" The negative intended to be reduced is then arranged verti- 

 cally, with its centre in the axis of the microscopic body, at a dis- 

 tance of from two to four feet from the lower object-glass, and 

 with a convenient screen of card, wood, or thick paper, to cut off 

 any extraneous light that would otherwise pass beyond the limits 

 of the picture. 



" A small camphene-lamp is employed for the purpose of illumi- 



