48 HOW TO SEE WITH THE MICROSCOPE. 



made for durability, and not liable to get out of order, 

 and is provided with means ot compensation for wear. 



It has rack and pinion for coarse and micrometer 

 screw for fine adjustment, the latter being placed in 

 front of the body, as has been usual in first-class instru- 

 ments, on the Jackson model. It is furnished with 

 graduated draw-tube ; sub-stage with rack and pinion, 

 and centring screws for accessory apparatus ; plane and 

 oncave mirrors on double-jointed arm; Tolles' thin 

 stage, admitting light of great obliquity ; with rectan- 

 gular movements by screw and rack and pinion, and 

 rotation on the optical axis of about 270. 



Mr. Tolles makes a modification of this sized stand, 

 the stage being carried by friction rollers, and having 

 entire rotation on the optical axis. The cost of the in- 

 strument is thereby somewhat enhanced. 



TOLLES' LARGEST "A" MICROSCOPE 



weighs twenty pounds, and is one of the largest and 

 most solid instruments extant. The stage is six inches 

 in diameter, and makes a complete revolution on the 

 optical axis. The whole instrument rotates on a stout 

 plate graduated to degrees, and is similar in all respects 

 of style and construction to the " B" stand. 



Either of the two stands named, made by Mr. Tolles, 

 may be unhesitatingly pronounced first-class. The work- 

 manship is of the very highest order ; the circular stao-e 

 can be so nicely adjusted as to allow of an entire revo- 

 lution, under a one- twenty-fifth objective, without the 



