OF THE MICROSCOPE. 75 



to the naked eye. Consequently, when these high powers are 

 used, it becomes very difficult for beginners to place the object 

 properly under the microscope, for, as will be readily seen, unless 

 it is adjusted with a variation less than the one-hundred-and- 

 fiftieth of an inch, it cannot be seen at all. 



The lowest powers that will show satisfactorily certain well- 

 known objects, are about as follows: The scales, or so-called 

 feathers on the wings of most butterflies can be very well seen 

 with a power of 25 diameters; under the same power, the eye 

 of a fly shows very distinctly the several smaller eyes, or ocelli, 

 of which it is composed; the individual corpuscles or globules 

 of the frog's blood can be distinguished with a power of about 

 35 diameters, human blood requiring 40 to 50; to show dis- 

 tinctly the form, etc., of these same corpuscles requires a power 

 of 200 and upwards. The same may be said of starch granules. 

 Human hair and wool may be seen very satisfactorily under a 

 power of 100 diameters, the former appearing like a cord, 

 a quarter of an inch thick. In order to show the peculiar char- 

 acteristics of these fibres, however, the lenses must be good. 

 Cotton and flax can be readily distinguished under a power of 

 80 diameters. 



A question very frequently asked in regard to cheap micro- 

 scopes is, Will they show the animalcules in water? And in 

 almost all the advertisements of cheap microscopes, we are told 

 that they will do this. Now, good well water does not contain 

 animalcules, that can be seen with ordinary microscopes. It 

 is only in stagnant water that they are found, and many of 

 them can be seen with the naked eye, without the use of any 

 microscope whatever. Others require the use of microscopes 

 having powers a hundred fold greater than that of the best 

 microscopes in ordinary use. It is evident, therefore, that 

 such statements are worthless as affording any indication of 

 the character of a microscope. A microscope magnifying fif- 

 teen to twenty diameters will show objects that are perfectly 

 invisible to the naked eye, and with fifty diameters, provided 

 the definition is good, we can obtain a very interesting view of 

 many of the most beautiful objects described in the books, and 

 sometimes called animalcules, such as the Volvox Globator, the 

 larger Vorticelli, etc., etc. 



