336 



THE AMERICAN MONTHLY 



[Nov 



densing bull's eye, and a plano-convex lens, turned in its 

 proper position, t, as a secondary condensing lens was 

 fitted to a double-jointed arm. The illuminating appar- 

 atus was therefore suitable for opaque objects, and must 

 be regarded as being very complete and efficient in its 

 day. 



Fig. 4 shows Divini's mi'iroscope (1667). The interest 

 in this instrument is not in the mount, which is of the 

 crudest form, but in the optical part, for in place of the 

 biconvex eye lens two plano-convex lenses, with their 



6 



convex surfaces in contact, were used. This plan would 

 halve the amount of the si-)herical aberration. 



Fig. 5 exhibits an improvement on the preceding form, 

 by Cherubin d'Orleans (1671). The body was more rig- 

 idly mounted by the enlargement of the tripod foot. A 

 screw movement was fitted to the stage for focussing. 

 In the optical part there is an erector. Chei-ubin 

 d'Orleans was the first to apply an erector to his monoc- 

 ular microscope, and he was also tlie first to construct a 

 binocular microscope. The binocular instrument woukl, 

 according to the drawing, have given a pseudosteieo- 

 scopic image. 



