44 



THE MICROSCOPIST. 



Fig. M. 



Erector. This is sometimes supplied with the best instru- 

 ments. It consists of a pair of lenses acting like the erecting 

 eye-piece of the telescope. It is applied to the draw tube at 

 the end of the eye-piece towards the object-glass. It is only 

 used when it is desired to dissect with the compound micro- 

 scope, as, without it, the position of the object appears re- 

 versed. 



Condensing Lens and Lamp. The Wollaston Condenser, 

 &c., is designed to concentrate the light which comes from the 

 mirror, directly upon the object; but the condensing lens and 

 lamp is used either for opaque objects, or to condense the light 

 upon the mirror itself. Two such lenses, as in the figure, are 

 generally used. Dr Goadby informed me, that after many 

 experiments he has found a bull's-eye lens, of three inches 

 focal length, the most efficient for the larger lens ; and after 

 several trials with different sorts of lenses I am disposed to 

 agree with him. Fig. 15 illustrates one mode of using the 

 condensers upon opaque objects. A, is the bull's-eye lens, 



