ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



G83 



of the apparatus by pasting on an additional piece of card of the 

 shape bdfg, and all the surfaces except the mirror should be 

 blackened with indian ink. 



"Dimensions: — ab and cd, also ah, bi, gh = 30 mm.; bg, df, 

 and the corresponding sides of S = 37 mm. ; the mirror less by the 

 thickness of the card — h c, i d, and hf (in my apparatus made for 

 Oberhiiuser's eye-piece = 10 mm.) will vary according to the size of 

 the eye-piece. Diameter of the hole in the mirror S = 3 mm. Dis- 

 tance of its upper edge from the left side of the mirror = 19 mm., 

 angle fde = 157°, dee = 36°, cef= 130°, efd = 37°." 



Bausch and Lomb Optical Co.'s Fine Adjustment* — Fig. 126 

 represents the original of the fine-adjustment referred to at Vol. I. 

 (1881) p. 110. Two strong parallel blades of finely tempered steel, 

 a a, are securely fastened on 



one end to the back of case Fig. 126. 



d, on the other to the arm e, 

 which carries the rack and 

 pinion, b shows the micro- 

 meter screw, which is fitted 

 to the upper part of the 

 upright arm c, /is the pinion, 

 g the rack and slide, h the 

 tube. Two screws fasten the 

 adjustment case d to the 

 pillar c. An arm projects 

 from the part e and passes 

 into a recess in the pillar c. 

 The springs support the 

 entire body, and as their 

 tension is upward, the pro- 

 jecting arm bears continually 

 against the micrometer screw 

 b, and it is evident that the 

 distance traversed by the 

 screw involves the same 

 movement of the arm e, and 

 consequently the body. The 

 only points of contact are at 

 the ends of the springs a, a, 

 where they are fastened re- 

 spectively at d and e, and on 

 the micrometer screw, and 

 as in the former there is 



absolutely no friction, there is no wear ; while that which may 

 eventually take place in the latter is taken up by the force of the 

 springs. 



The points of excellence claimed by the makers for this adjust- 

 ment over all others, are the following : — 



* From the Company's Price List, 7th ed., 1882, pp. 4-5 (1 fig.). 



