On the Evolution of the Fine Adjustment . By E. M. Nelson. 371 
and precision with which this fine adjustment still works ; one 
revolution of the milled head gives a movement of 1/670 in. 
We now come to the short-lever fine adjustment on the nose-piece, 
in connection with which there are two points I am quite unable to 
elucidate, viz. the name of the inventor, and the date of its intro- 
duction. The first time we meet with it is in a description of a 
Microscope made by Andrew Ross (42), published in 1839 ; but we 
know that it was the common form of adjustment for the Microscopes 
of nearly all the makers about that date. Powell must, however, 
he excepted, as he used it only for his cheapest form of stand. 
Although it was a most inefficient form of fine adjustment, it was 
very generally employed for upwards of forty years. The lever was 
one of the second order. 
On the Continent, from about 1835, we meet with a number 
of Microscopes which had tilting stage fine adjustments (47). One 
side of the stage was hinged, while the opposite side was capable 
of being either raised or lowered by a screw. This was the usual 
form, but there were some modifications of this plan. Owing to 
the cheapness of this crude construction, this fine adjustment was 
very popular on the Continent ; it has now quite disappeared, and 
it had no influence whatever on the evolution of the Microscope. 
In 1841, three Microscopes were purchased by this Society ; those 
made hy Messrs. James Smith (43) and Andrew Ross (44) had 
short lever nose-piece fine adjustments ; but Powell’s (45) was on the 
stage-focussing principle just described. One revolution of the milled 
head in J. Smith’s Microscope gives a movement of 1/150 in. to the 
nose-piece, and 1/120 in. in the Andrew Ross. 
In this same year (1841), Powell (46) had brought out a new 
kind of fine adjustment, which was adapted to a Microscope with a 
Lister limb ; this fine adjustment had a steel cone at the end of the 
micrometer screw, this cone acted on a nose-piece against the pressure 
of a spring. Powell, however, soon abandoned this form cf Micro- 
scope with the Lister limb in favour of the bar movement. In 1843 
he introduced his tripod foot holding a long lever bar movement 
Microscope (48). The long lever was of the first order, and was 
actuated by an advancing cone. Subsequently, about 1847, he 
abandoned the advancing cone and placed the micrometer screw on 
the top of the bar (49), immediately behind the screw forming the 
pivot and attachment of the bar to the prism-shaped rod ; this is the 
fine adjustment that is still made by the same firm (one revolution 
causing a movement of 1 /200 in.). 
In 1843, but subsequent to the publication of Powell’s long lever, 
Andrew Ross (50) brought out his long lever-bar movement; the 
lever being of the second order ; several examples of this we have 
in our cabinet ; and they are from time to time used in this room. 
In this country from 1843 to about 1870, we had four types of 
fine adjustments, viz. (1) Powell’s long lever of the first order (49) ; 
