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Transactions of the Society. 
(2) Ross’ long lever of the second order (50) ; (3) short lever nose- 
piece (42) ; (4) direct-acting screw on the Hartnack model (51). 
About 1860, Nobert introduced the differential screw, which was 
reinvented by the Rev. James Campbell (52), 1886, and is now 
used with satisfactory results by Messrs. Baker and Swift, one revolu- 
tion causing a movement of 1/200 in. About 1878, Ross (53) 
adopted the Zentmayer (54), 1876, an American form of Micro- 
scope ; it did not however prove successful. In this Microscope the 
whole body, instead of the nose-piece only, was moved by the fine 
adjustment. 
A direct-acting screw fine adjustment of a novel form was intro- 
duced by Messrs. Seibert and KrafFt (55) in 1876; the body was 
attached to the vertical pillar by a parallel movement, precisely 
similar to that of a common parallel ruler. A direct-acting screw 
pressed, through a loose intermediate piece, on an arm rigidly fixed 
to the body. The ingenious part of this fine adjustment is the 
loose intermediate piece, which compensates for any lateral move- 
ment. 
In 1876, Messrs. Bausch and Lomb (56) patented a direct-acting 
screw fine adjustment, in which the body was attached to the limb 
by two horizontal and parallel steel springs, the body being moved 
by a screw working directly upon it. This plan was merely a 
simplification of the previous form. It was further improved in 
1887 by Messrs. Swift and Son (57), who added a lever movement 
to it. 
In 1881, Messrs. Swift and Son (58) introduced their vertical 
long lever fine adjustment, which worked only the nose-piece, one 
revolution causing a movement of 1/300 in. Subsequently this was 
constructed so that it moved the whole body. The manner in which 
this was effected differed from that of Zentmayer’s ; for Swift supplied 
a wide slide with V-grooves, thoroughly well sprung, so that a steady 
and equable movement was obtained (59). 
In 1886, Messrs. Zeiss (60), who had hitherto used the Hartnack 
form of fine adjustment, altered it by making a left-handed micro- 
meter-screw, which had a hardened steel point, press on a hardened 
steel plate. This plan, of course, takes all lateral strains off the 
screw. In this, one revolution of the milled head causes a move- 
ment of 1/101 in. ; in Reichert’s, 1/85 ; and Leitz, 1/51. In America, 
where the Continental Microscope has been largely adopted, Messrs. 
Bausch and Lomb have given a speed of 1/51 in. for each revolution 
of the milled head; this is seven times quicker than Watson’s 
lever. 
In 1889, Messrs. Watson and Son (61) adopted the Powell fine 
adjustment, with the exception that the lever raised the whole body, 
instead of only the nose-piece, in the same way as Swift’s second 
form of vertical lever did. In 1892, Watson’s fine adjustment was 
altered by making the micrometer-screw a left-handed one, so that 
