426 



Notes. 



Fig. 105. 



Fig. 106. 



trade, and that Mr. Valentine, in getting hi in to carry out his ideas, 

 preferred to deal direct with the actual maker rather than through 

 any of the retail opticians, who merely engraved their names on the 

 instruments made by Messrs. Ross, Powell, and others. 



Mr. Valentine's Microscope was a very good one in its day. Ft has 

 been repeatedly figured, but important details in its construction, 

 which have had much influence on the evolution of the Microscope, 

 have been passed over without notice. 



Description of this Microscope. — The foot was a flat folding 

 tripod, fig. 104 — a common form at that time ; it was subsequently 

 altered to a solid flat tripoi. Stage — mechanical with slow rectangular 

 movements, actuated by direct-acting screws. 



This movement was a sort of fine adjustment stage movement, the 

 coarse adjustment being the movement of the lens over the object; it 

 should be remembered that for about three-quarters of a century it 

 had been the custom to fix the object and move the lens over it. 



Illumination. — Wollaston's illumi- 

 nating apparatus, fig. 105, or a modifica- 

 tion of it, as shown attached to the 

 Microscope in fig. 104. 



Focussing. — These movements were 

 three in number : — 1st, by drawing out 

 the inner triangular bar ; 2nd, by rack- 

 and-pinion work, which moved the middle 

 triangular bar ; 3rd, by fine adjustment 

 screw, which moved the outer triangular 

 bar. So in principle the movement is 

 not unlike that of the modern Continental 

 Microscope, where the body and coarse 

 adjustment are carried by the fine adjust- 

 ment screw. 



This Microscope was, like many of 

 that date, both single and compound. 

 The lens-holder, for either a single lens 

 or a Wollaston doublet, is shown in fig. 

 106. These lenses, although non-achro- 

 matic, were excellent; their fields and 

 apertures were small; nevertheless they gave very good images. I 

 have in my cabinet a Wollaston doublet which shows tubercle bacilli. 

 The lens-holder was attached to the top of the inner triangular bar 

 by means of a conical pin ; the lens was therefore capable of a motion 

 in arc over the preparation as well as that given to it by means of 

 the extension rackwork. This movement — a very convenient one for 

 a simple dissecting Microscope — owes its origin to Ellis's Aquatic 

 Microscope, made by J. Cuff in 1755 ; afterwards [Benj. Martin was 

 the first to add rack-and-pinion to the extension and a worm-wheel 

 to the tangential movement. 



