8 THE STRUCTURE OF 



Objects, when placed under the Microscope, are 

 of two kinds, either transparent or opaque. When 

 they are opaque, they may either be placed upon 

 the slips of glass, or put between a small pair of 

 forceps which are fixed to the stage of the Micro- 

 scope, and the light of a window or lamp allowed 

 to fall upon them. This is not, however, sufficient, 

 generally, to examine things with great accuracy ; 

 and an instrument called a condenser is provided 

 for this purpose. It consists merely of a large 

 lens, which is sometimes fixed to the stage, or has 

 a separate stand. Its object is to allow a concen- 

 trated ray of light to be thrown on the opaque 

 object whilst under the object-glass of the Micro- 

 scope. This is called viewing objects by reflected 

 light. 



Transparent objects, on the other hand, are 

 viewed with transmitted light : and here again the 

 natural diffused light of day, or of a lamp, is not 

 sufficient ; so that all Microscopes are provided 

 beneath the stage with a mirror, plane on one 

 side and concave on the other. The object of this 

 mirror, which is called the reflector, is to catch the 

 rays of light and concentrate them on the object 

 under the Microscope. The rays of light thus pass 

 through the object, and its parts are seen much 

 more clearly. 



Another convenient piece of apparatus is an 

 animalcule-cage. This consists of a little brass box, 

 inverted, to the bottom of which is attached a piece 

 of glass. Over this, again, is placed a lid or cover, 

 with a glass top. The cover can be made to press 

 on the glass beneath, and an object being placed 

 between the two glasses, can be submitted to any 

 amount of pressure thought necessary. This is a 

 very important instrument for examining minute 

 Crustacea, animalcules, zoophytes, and other living 



