152 MICROSCOPIC ILLUSTRATIONS. 



thing connected with them, till every point is effected in 

 the best possible manner ? These instruments have under- 

 gone a complete revolution in their optical parts, and 

 become truly dignified and respectable : assuredly their 

 mechanical structure should correspond with the advance 

 which has taken place in their optical constitution. 



However, like other things, they are varied in their 

 construction to serve particular purposes. Thus, if made 

 merely for commerce, or to look at, or to wear in the 

 waistcoat pocket, like a snuff-box, they must evidently 

 be made on a plan quite different from that required for 

 scientific observations. 



I pretend not to meddle with matters concerning com- 

 merce; the trade understand them far better than I do, 

 and shall therefore merely observe, that several indivi- 

 duals experienced in business have assured me, that the 

 first thing to be considered in the construction of a mi- 

 croscope is its price ; and the second, the size of its case, 

 and how it is to look when packed in it, with all its little 

 eye-traps and trinkets about it. It is frequently sold in 

 two minutes, long before the merits of its construction 

 can be known; therefore one kind is just as good as 

 another, the public at large being no judges or con- 

 noisseurs in such matters. 



Again, instruments may be made expressly for trans- 

 parent objects, or opaque ones, or even some particular 

 class of those bodies, for lamp-light only, or for that of 

 the atmosphere, for drawing, for public exhibition, &c. 

 all of which circumstances will produce a variation in 



