THE MICROSCOPE. 11 



may require for the elucidation of the structure 

 undergoing examination. 



We next come to the stand, which, though the 

 most mechanical, is at the same time a very impor- 

 tant part of the Compound Microscope. On the 

 solidity and steadiness of this portion of the instru- 

 ment depends in a great measure its utility. The 

 form generally adhered to is that represented in our 

 diagram (fig. 1, p. 5.) It consists of a tripod base, P, 

 from which rise two flat upright pillars, 0. Between 

 these, on the two hinge-joints shown at L, is sus- 

 pended the whole of the apparatus already described : 

 namely, the body carrying the lenses, the arm to 

 which it is attached, the stage, and the mirror 

 underneath it. By this contrivance the Microscope 

 can be inclined at any angle between a vertical and 

 horizontal position an advantage which can be duly 

 appreciated by those who work with the instrument 

 for two or three hours at a time. Close to the 

 points of suspension are the milled heads, M ; these 

 are connected with a pinion working in a rack cut 

 in the stem, E. By turning the milled heads the 

 tube is made to approach or recede from the stage 

 until the proper focus of the object-glass is found. 

 This is termed the coarse adjustment, and is gene- 

 rally used for low powers, where delicate focussing is 

 not required. But when high magnifying powers 

 are used, that require a far greater degree of pre- 

 cision, we have recourse to the fine adjustment, N, 

 which consists of a screw acting on the end of a 

 lever. The head of the screw by which motion ic 

 communicated to the object-glass is divided into ten 

 equal parts, and when caused to rotate through any 

 of its divisions slightly raises or depresses the tube, 

 carrying the objective with it. As the screw itself 

 contains just 150 threads to an inch one revolution 

 of its head will cause an alteration of the 150th 



