1 72 T1IK H1STOKY .\ND DEVELOPMENT UF THE MICEOSCOPE 



levers, h. li. which in turn press the arched piece with its appendix f 

 on 1u tin' prism support. The principal screw has three threads 

 to the imllemeTer. which by the lever> is reduced by about one 

 third. The pointer for reading the micrometer scale on the 

 milled head is conveniently arranged so that it can be changed to any 

 iL'iire on the ><-ale. The speed of the adjustment is ., } Tl th inch to 

 one r<'\-olntion of the milled head. 



\\'e may now profitably consider the best forms of fine adjust- 

 ment thai apply to the Li>ter model, and one of the steadiest and 



FIG. 184. Nelson's model will, 

 adjustment screw to the left h.- 



FIG. 135 (1885;. 



licateofthe.se is that de\i-ed by Messrs. Watson and Sons. 



I'lie entire body i> raised or |ov.,-r.-d by means of a milled head fixed 



ha\ini.' ;i li;irlcn-d -r,.,.| point, acting on a lever with 



aii.l hii/hly poli>h..i| against a point 



-li'l'-. in --tailed fitting, about 



hown in fig. 132. Jiy 

 :l"d li-ad ih- hard steel I. ... I;, which has its fulcrum 



