MOUNTING OF OBJECT-GLASSES. 
41 
the tliin glass which covers the object. The one inch and two 
inch objectives do not require this adjustment. 
Figure 17 shows the method of mounting the best object- 
glasses, with Mr. Wen- 
ham’s adjustment for 
the thickness of glass 
cover, A being a longi- 
tudinal section, and B 
an exterior view of the 
same. 
The anterior com- 
pound lens is perma- 
nently fixed to the out- 
er tude, or that part of 
the mounting which 
connects the objective 
to the body of the microscope, while the middle and posterior 
combinations are set in a tube which slides wuthin the other. 
A revolving collar, with its milled edge 5, is attached by a 
screw to the inner tube, the screw passing through a slide in an 
inclined slit in the tube which carries the anterior combination. 
When the collar is revolved, the screw and slide moving in the 
inclined slit, the inner tube, with the posterior and middle com- 
pound lenses, is made to approach or recede from the anterior 
combination. 
The slit in the outer tube is so much inclined that a quarter 
of a revolution gives to the inner tube the greatest extent of 
movement that is ever required. This movement of the middle 
and posterior combinations effects the adjustment required by 
covering the object with glass of any required thickness. The 
point on the collar marked uncovered'^^ is the point of adjust- 
ment which gives the most perfect definition of an uncovered 
object; the part marked ‘Hhin glass’^ indicates the correction 
for glass of medium thickness. Between these two points are 
ten or more divisions, and several equal spaces are marked oft* 
beyond this point. 
This graduation is exceedingly convenient for many purposes, 
CATALOGUE OF ACHROMATIC MICROSCOPES. 
