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by splitting tlie screw-hole, and making the two halves spring towards 
each other, so as to pinch the screw between them. A better mode- 
than this is shown in the figure ; on the screw is placed a separate 
screwed nut, a little way below the bottom of the sliding tube, and two 
pins or screws pass through it into the tube, merely to prevent its 
turning round. This nut is to be urged from the tube by interposing 
a spiral or other sort of spring between them : this arrangement 
will keep the tube always pressing upwards against the screw 
threads.” 
For certain other reasons Yarley modifies in a slight degree this 
plan ; it is not, however, sufficiently important to quote at length ; but 
further on he points out that the graduation of the milled head will 
enable the thickness of objects to be measured. So in this first 
Microscope of Yarley ’s design and make, we have no less than four 
contrivances, which are in use to-day : — 1st, calotte rotating nose- 
piece ; 2nd, cylinder diaphragm ; 3rd, sprung fine adjustment ; 4th, 
graduation to milled head of fine adjustment. All these four items are 
original, and the first instances of their use in any Microscope, made 
either here or on the Continent. 
The next Microscope we come to was made in March 1831, but 
subsequently to that of Varley’s, as we shall presently see. It was 
designed by Mr. W. Valentine, of Nottingham (40), to whom a 
large silver medal was granted by the Society of Arts, and was made 
by Andrew Ross. The Microscope was both simple and compound, 
it was non-in clinable, the foot was a folding tripod, the coarse adjust- 
ment was accomplished by racking a triangular bar out of a vertical 
post, the stage was strengthened by struts for dissecting purposes, 
and was fitted with mechanical rectangular movements. The fine 
adjustment was a direct-acting screw, fifty threads to the inch (sug- 
gested by Dr. Solly), actuated by a milled head placed at the bottom 
of the pillar, the milled head being graduated into 100 divisions. 
Now we come to the important part, which I will give in Mr. Valen- 
tine’s own words: “ . . . . end-shake being prevented by the spring. 
The action of this sort of spring is fully explained in the account of 
Mr. Yarley ’s Microscope.” So here we have a Microscope designed 
by Mr. Valentine, and made by Andrew Ross, in the description of 
which there is an acknowledgment that the springing of the fine 
adjustment is due to Mr. Yarley. 
The next fine adjustment we have to consider was applied to the 
stage by H. Powell (41) ; for this the Society of Arts, in 1834,. 
awarded a silver medal to him. The method by which this adjust- 
ment was effected was quite novel, for by means of a micrometer 
screw three wedges were moved underneath a Turrell stage, causing 
it either to rise or fall with a very slow parallel motion ; one turn 
of the micrometer screw causing a movement of 1/300 in., which is 
one-sixth that of Valentine’s. One of these Microscopes made before 
the year 1811 is in my possession ; and I can testify to the steadiness 
