Francis Watkins' Microscope. By E. M. Nelson. 139 



mirror. This is, so far as I know, the earliest example wherein this 

 design is to be seen ; and it should be borne in mind that this 

 design is the basis upon which the modern Microscope is built. 

 This plan was afterwards adopted by Adams in his " Variable " 

 Microscope,* 1771 (fig. 28), which he tells us was designed by a 

 nobleman, who did not wish his name to be published. I was of 

 opinion, until I had seen the Watkins Microscope, that the 

 " Variable " of the anonymous nobleman was the prototype of the 

 modern Microscope, but it is clear that the " Variable " is nearly 

 a quarter of a century later than this signed and dated example 

 of Watkins' Microscope. The coarse-adjustment focusing arrange- 



Pig. 27. 



ment of Watkins' Microscope differed from those of its day, 

 inasmuch as the stage, which slides up and down the limb, is placed 

 to a number similar to that of the power used (in fact, there are 

 two sets of numbers, marked S and D : S indicating the set of 

 numbers to be used with the simple, and D those with the " double," 

 or compound, Microscope), whereas in earlier instruments it was 

 the body, and not the stage, that was moved in this way. Watkins' 

 Microscope has a neat form of spring-clamp to fix the stage in 

 a definite position. The fine-adjustment, which in Watkins' 

 Microscope is worked by a screw at the end of the limb, moves 



Micrograpkia Illustrata, ed. 4, plate ii. 



L 2 



