THE MICROSCOPE. 17 



latter are made to diverge, and when pushed in 

 they converge. In this way any intermediate 

 distance can be obtained to suit every kind of 

 vision. 



Where a Binocular Microscope is in daily use it 

 will sometimes be necessary to withdraw the prism 

 from the tube, to cleanse it from dust and other 

 impurities gradually contracted by use. Whenever 

 this may be necessary great care should be taken 

 to employ no substance likely to scratch its highly 

 polished surfaces; for on these being preserved intact 

 in a great measure dej^nds the efficiency of the in- 

 strument. We know of nothing better adapted for 

 removing impurities than a clean silk or cambric 

 handkerchief, which, when not in use, should be kept 

 in a closely-fitting drawer, to protect it from dust. 



There seems to be little doubt that this lately 

 improved form of the Compound Microscope will 

 eventually supersede all others. This opinion also 

 seems to be entertained by the inventor himself, 

 whose words we quote : — 



" The numerous Microscopes that have been 

 altered into Binoculars, in accordance with my last 

 principle, and also the large quantity still in the 

 course of manufacture, will, I think, justify me in 

 making the assertion, without presumption, that 

 henceforth no first-class Microscope will be con- 

 sidered complete unless adapted with the Binocular 

 arrangement." 



The Compound Microscope is now, undoubtedly, 

 one of the most perfect instruments invented and 

 used by man. In the case of all other instruments, 

 the materials with which they are made and the 

 defects of construction are drawbacks on their per- 

 fect working ; but in the Compound Microscope 

 we have an instrument working up to the theory 

 of its construction. It does actually all that could 



C 



