ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



629 



smallest power, and, possessing a long focal distance, are of use for all 

 kinds of objects, transparent or opaque. 



" There are two eye-pieces, each with two lenses, which can be 

 successively placed at A at the end of the tube [fig. 154] made up of 

 the two parts B and C, or simply at the end of C. Thus with the four 

 series of objectives, figs. 2, 3, 4, and 5 applied separately at D, sixteen 

 different magnifying powers are obtained. 



" Taking away next the tubes B and C and the eye-piece A, leaving 

 only the milled head G, with one or more objectives, these latter act as 

 common lenses (or " loupes "), and the Microscope — in that case equiva- 

 lent to a simple Microscope — may be used in observing large bodies and 

 for their preparation and dissection. 



11 Opaque bodies are illuminated by means of the lens F, which is so 



%/*■ 



V* 



Fig. 155. 





A,V 



y 



<? 



s 



UME 



V5 



H^i 





inclined as to throw the light from a lamp or the daylight upon the 

 object. 



" Transparent bodies are illuminated by the reflection from the 

 mirror L underneath, through the lens H. This lens slides along a ver- 

 tical arm, and can be approximated to or removed from the object and 

 placed more or less obliquely to it. Clearness of vision depends chiefly 

 on the satisfactory placing of the illuminating lens, and it is well to get 

 considerable practice, so as to ascertain the most favourable position for 

 illumination, according to the nature of the object and the particular 

 series of objectives which is in use. For the weaker objectives the lens 

 H is usually covered by the black diaphragm placed above it. 



" There is a flat ground glass which is introduced between the little 

 springs under the stage only when it is desired to use direct sunlight as 

 an illuminant, so as to increase the brilliance of the bodies without 

 burning them. 



" All the glasses, eye-pieces, and objectives alike, are kept bright by 

 cleaning with the reverse side of a thin piece of glove-leather. This pre- 



