50 THE MICROSCOPE 



form to the Royal Microscopical Society's standard. 

 It must also be provided with good lenses and a suffi- 

 ciently large stage. The details of its component parts, 

 to which attention must be specially directed, are as 

 follows : 



1. The Base or Foot (Fig. 40, a). Two elementary 

 forms the tripod (Fig. 41, a) and the vertical column 



FIG. 41. Foot, three types. 



set into a plate known as the "horse-shoe" (Fig 

 41, b) serve as the patterns for countless modifica- 

 tions in shape and size of this portion of the stand. 

 The chief desiderata stability and ease of manipula- 

 tion are attained in the first by means of the " spread " 

 of the three feet, which are usually shod with cork; in 

 the second, by the dead weight .of the foot-plate. The 

 tripod is mechanically the more correct form, and for 

 practical use is much to be preferred. Its chief rival, 

 the Jackson foot (Fig. 41, c), is based upon the same 

 principle, and on the score of appearance has much to 

 recommend it. 



2. The body tube (Fig. 40, b) may be either that 

 known as the "long" or "English" (length 250 mm.), 

 or the "short" or "Continental" (length 160 mm.). 

 Neither length appears to possess any material advan- 

 tage over the other, but it is absolutely necessary to 

 secure objectives which have been manufactured for 

 the particular tube length chosen. In the high-class 

 microscope of the present day the body tube is usually 



