Microscopes of Powell, Ross, and Smith. By E. M. Nelson. 427 



The compound body was attached to the inner triangular bar 

 by a conical pin, in the same manner as the lens-holder (fig. 107).*" 

 The important part of the Microscope lies in its fine adjustment ; 

 the screw with 50 threads to the inch had its head divided into 100' 

 parts, and placed below the foot. This Microscope resembled, in three 

 points, Adams's Universal Microscope of 1746, for both had upright 

 pillars, both flat folding tripod feet, and both had the heads of their fine 



Fig. 107. 



Fig. 108. 



MkuttMi .i^ttmmiiuiimi^iiiiumSm^ 



adjustment screws below the bases of their pillars ; Adams's, however, 

 was a stage focusser. This is the first instance we meet with of the head 

 of a fine adjustment screw divided for micrometrical purposes ; and it 

 was the suggestion of Mr. R. H. Solly, whose liberality in defraying the 

 cost of the plates illustrating these early Microscopes enables us to 



* Mr. J. Mayall, junr., figures this Microscope, with the compound body and 

 Wollaston condenser attached, iu the Cantor Lectures of the Society of Arts for 1888 

 p. 14, fig. 2D, but he has failtd to note its identity with Valentine's Microscope. Had 

 he known that an important feature in this Microscope was copied from a Micro- 

 scope designed by C. Varley, he would probably have modified his adverse criticism 

 on the latter's work. 



