ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



555 



Fig, 99. 



sliding plate is the essential addition to the usual racked slide in the 

 application of the new fine-adjustment to the suhstage. The range of 

 motion is about | inch — the 

 difference in radius between the 

 smaller and larger ends of the 

 steel cone. 



Mr. Nelson states that he has 

 found the fine-adjustment on the 

 substage of service in difficult in- 

 vestigations with the condenser 

 in the axis. By this means he 

 can readily exhibit the transverse 

 lines of A. pellucida without any 

 diaphragm. 



Sidle's Centering Substage, 

 — We gave a figure of Messrs. 

 Sidle's " Iris " diaphragm in Vol. 

 III. (1880) p. 1053, and briefly 

 alluded to the centering arrange- 

 ment of the substage as " a short 



bar working with a loosely fitting slot, that can be clamped beneath," 

 which is characterized as a somewhat primitive contrivance. Messrs. 

 Sidle now adopt in their " Acme No, 2 Binocular," the method of 

 centering shown in Fig. 100, the special feature of which is that the 

 substage motions are controlled by 

 two milled heads (right and left) on 

 the arm or bar-attachment at the 

 back of the substage carrier, racking 

 on the swinging tail-piece. By this 

 system the usual outer substage-ring, 

 with its projecting centering screws 

 (so generally adopted in America), is 

 done away with. The forward mo- 

 tion is given by the left-hand milled 

 head acting on rackwork ; the lateral 

 motion by the right-hand milled head 

 acting on a pointed screw against a 

 U-shaped spring that presses the 

 slide towards that side, the fixed end 



of the spring being attached to the main base- or angle-plate racking 

 on the tail-piece. 



We have not yet seen this mechanism, but with good workmanship 

 we should anticipate the plan to be practical — certainly much better 

 than the former system of centering by the rough process of pushing, 

 pulling, and clamping by hand, which did not suggest the possibility 

 of accurate centering. 



Mounting for the "Woodward" Prism.*— Dr. J. Edwards Smith 

 recommends the form of mounting the " Woodward " prism shown in 



* 'How to Work with the Microscope ' (Svo, Chicago, 18S0) p. 171 ct scq. 



Fig. 100 



