PRACTICAL MICROSCOPY. 



in the pocket when field hunting, will prove of invaluable 

 assistance to the student. The most useful powers will be 

 found in those amplifying 1 5 and 30 diameters : the former 

 serves well for the examination of mosses, ferns, lichens, 

 algae, and such members of the animal world as can be 



FIG. 2. 



recognised by the aid of a 3-inch objective and the A 

 eye-piece, to which combined, it is about equal in power ; 

 whilst the smaller glass, giving greater amplification, 

 answers admirably for micro-fungi, minute algae and 

 lichens, and those forms of animal life for which a i-J-inch 

 objective is desirable. 



If the reader refers to any work treating upon optics, he 

 will find that convex lenses yield images in two distinct 

 manners virtital images and real images. A double 

 convex lens, when used as an ordinary magnifying glass, 

 produces a virtual image which is erect and larger than 

 the object, as may be seen by reference to Fig. 3. 



The greater the convexity given to the surfaces of the 

 lens, the more will it amplify, and it may also be said 



