220 



DR. SCHACHT, ON THE MICROSCOPE. 



rack and pinion, and a traversing motion on a pivot, by which means 

 the lens can be carried in auj' direction over the stage. The adjustment 

 of the focus is effected by the large milled head at the side. This instru- 

 ment is usually furnished with lenses of 1 inch, 2 inch, i inch, and 1-lOth 

 inch focal lengths, and sometimes with a WoUaston's doublet. The doub- 

 let may well be dispensed with, if the observer is possessed of a compound 

 achromatic microscope. In carrying on delicate dissections with this 

 microscope, it is advisable to make use of the arm-rests, which will be 

 described hereafter in the chapter on accessory instruments. Mr, Ross's 

 1 inch achromatic object-glass may be used in dissecting with this instru- 

 ment, and will be found most agreeable. 



Fig. 15. 



Fig. 16. 



Figs. 16, 17, and 18, represent another form of dissecting microscope, 

 called " Quekett's Dissecting Microscope," lately produced by Mr. High- 

 ley. Fig. 16 shows the instrument 

 folded up with an Indian-rubber band 

 round it, in a manner which admits of 

 its being carried in the jiocket. The 

 two wedge-shaped pieces of wood under- 

 neath unfold and form the legs (sec figs. 

 17 and 18). Fig. 17 shows the internal 

 arrangement and the manner in which 

 the mirror, lenses, and lens-holder are 

 packed away. The straight, flat bar, 

 on the right in fig. 17, serves to keep 

 -'--=^ the legs from closing together (see fig. 



18), and also as a support for the mirror, 

 wliicli slides into a piece of brass tubing attached to the flat bar. The 

 circular hole at tlie lower end of fig. 17 is another piece of brass tubing, 

 into which tlie lens-holder slides. 'I'he instrument is furnished with three 

 lenses, and is to be had at a moderate price. 



