On Microscopes in General. 6 



formed (as it were, in the air,} between the two lenses. 

 It is already larger than the object, and is further 

 magnified by the upper lens. A very great increase 

 to the magnifying power is thus obtained, but to ob- 

 tain it with perfect clearness, and with freedom from 

 various drawbacks and inconveniences, has long 

 exercised the cleverness of opticians. The combina- 

 tion of lenses next the object, called ' ' the object- 

 glass," requires great care and trouble in its construc- 

 tion. The proper length for the tube, and due form 

 for the upper set of lenses (or " eye-glass ") also 

 demand much attention ; but this care and attention 

 have not been bestowed in vain, as great excellence 

 has been attained. 



Compound microscopes bear a general resem- 

 blance to each other in external appearance, (see fig. 

 1, Plate I.,) yet a distinction may be made among 

 them into two principal classes; namely, the large, 

 substantial, and complete instruments, in which perfec- 

 tion has been the aim, and the smaller and lighter 

 ones, which have been made with a view to cheapness, 

 although no trouble has been spared to render them as 

 good as possible for the price. And for full information 

 about various simple and compound microscopes, with 

 most interesting details about their principle and con- 

 struction, I would refer the reader to Dr. Carpenter's 

 valuable book, " The Microscope and its Revelations." 

 While studying the opening chapters of that work, 

 the reader feels as if visiting the establishments of 

 various opticians, at home and abroad, arm-in-arm 

 with an ever ready exponent of every point of interest 



