On the Evolution, of the Fine Adjustment. By E. M. Nelson. 367 
scope was still made in 1798. In 1747 we have a stage focnsser by 
Adams ( 21 ), with the nut placed at the bottom of a vertical pillar; 
and in 1771 the variable Microscope (22), by the same maker, con- 
structed from the designs of a nobleman who did not want his name to 
be published. Here we have both a coarse and a line adjustment, but 
only one slide ; so that when the coarse adjustment is used, the fine 
adjustment has to be put out of action by releasing a clamping-screw ; 
also when the fine adjustment is clamped up for use, the rack of the 
coarse adjustment is obliged to turn the coarse adjustment pinion. A 
similar arrangement is found in a Microscope by Benj. Martin ( 23 ). 
In this same year, 1771, a very handy instrument called the ‘‘Com- 
pendious Pocket Microscope” was made by Adams ( 24 ), probably 
one of the best of these old instruments ; it was a body focusser by 
rack-and-pinion. In 1776 Benj. Martin ( 25 ) brought out a some- 
what more elaborate form, as a counterblast to Adams’s of 1771 ; one 
of these was presented by Dr. Ballinger to the Society at our last 
meeting. The Microscopes succeeding these were rack-and-pinion 
stage focussers ; an important example by Adams ( 26 ) was presented 
to the Society at the last meeting by Mr. J. M. Offord. This type of 
Microscope culminated in the “Jones’ most improved” ( 27 ) of 1798. 
The following Microscopes also had no fine adjustments: — Fraun- 
hofer's drum Microscope (1815) : this model was subsequently adopted 
by Chevalier (28), and Lerebours, of Paris, and about 1810 was a 
very popular form; Selligue’s ( 29 ), 1824, was a rackwork stage 
focusser; Lister’s (30), 1826, a rackwork body focusser; Goring’s 
( 31 ) “ Operative Aplanatic Engiscope” (March 1829) a body focusser 
by rack-and-pinion, a triangular bar racking, out of a cylindrical rod ; 
the first Microscope in which this excellent idea was carried out. In 
connection with this Microscope Dr. Goring makes this remarkable 
statement : “ If the present stand was made to operate solely with 
an engiscopic refracting body, it would be better to omit the rack- 
work of the upright bar altogether, and substitute a pinching- 
screvv for it, giving a fine movement to the body within the neck 
of the arm by a screw on Bamsden’s princple.” Now the “ screw 
on Bamsden’s principle ” was a differential screw ; so here we have 
the first suggestion of ils application to a Microscope. 
We will now examine some Continental models. Chevalier (32), 
1834, coarse adjustment to stage by rackwork, and fine adjust- 
ment to stage by screw, the screw being similar to Cuffs. Schiek 
( 33 ), coarse adjustment to body, and line adjustment to stage, screw 
action similar to Cuff’s. Pistor ( 34 ), a sliding coarse adjustment, 
fine adjustment by a clamping-screw fitted in a manner similar to 
the older forms of Benjamin Martin, and the variable Microscope of 
Adams, so that before using the sliding coarse adjustment, the fine 
adjustment had to be thrown out of action by releasing the clamping- 
screw. These Microscopes may be dated about 1830. Prof. Amici 
( 35 ) designed a - Microscope about 1835, with rackwork stage coarse 
