PRACTICAL MICROSCOPY. 



Microscopical research does not always require the aid 

 of expensive apparatus. It is very handy and often saves 

 time, no doubt, to have ready all those accessories so 

 ingeniously devised by the makers, for microscopists with 

 long purses ; but apparatus to answer the same purposes 

 may often be made by the ingenious worker, which, though 

 not possessing such a good appearance, serve just as well 

 as the more expensive articles. 



Many microscopists, after a few years' devotion to their 

 favourite instrument, find themselves encumbered with a 

 host of paraphernalia of no use to themselves or to any one 

 else, the cost of which might have been saved by con- 

 sidering beforehand the capabilities of the required appa- 

 ratus. As to instruments, each individual taste has to be 

 considered, some prefer one pattern and some another ; 

 but, after all, these matters are easily arranged if the 

 principle of construction is good. 



The main office of the microscope is that of enlargement ; 

 but this amplification of the image of an object must be 

 attained without distortion or the introduction of colours 

 not in the original, and it is because single lenses give 

 images blurred with spherical and chromatic aberration 

 that double and triple combinations are used in the con- 

 struction of all good microscopes. Single lenses are how- 

 ever very useful for general purposes: as a pocket lens, 

 it prevents the collection of much useless material during a 

 naturalist's rambles, and upon reaching home a further use 

 is found in its employment as an aid in dissecting or in 

 mounting the objects culled. The most useful magnifiers 

 are the ordinary watchmakers' or engravers' eye-glasses in 

 the usual horn mount, but their amplifying power should 

 not be too great or continued use may impair the eyesight. 



A combination of several single lenses, such as is shown 

 in Fig. i, is much used as a pocket magnifier for the field 



