ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 673 
between each foot. It has a joint for inclination, and the fine-adjustment 
is regulated by a micrometer-screw and large milled head. The large 
square stage has a distance of 2^ in. from centre of stage to limb, and 
allows a very large culture-plate to be examined. The under-stage is 
provided with a fitting of the full size, and is furnished with an im- 
proved form of iris-diaphragm enlarged or contracted by means of a 
handle-shown in the figure. Each instrument is provided with a plane 
and concave mirror. An Abbe form of condenser at once converts the 
instrument into a very efficient Microscope for bacteriology and other 
high power study. 
Fig. 115 shows a more expensive form of the same instrument. The 
difference is partly in the coarse adjustment, which here is a spiral rack 
and pinion. The draw-tube is engraved in millimetres, and at once 
records the exact amount of mechanical tube-length in use. Another 
addition is a rack and pinion focussing and screw centering substage ; 
the milled head of the focussing substage pinion is extended beyond the 
legs of the tripod, thus placing the focussing adjustment of the substage 
always within easy reach, even when the instrument is used in a vertical 
position. By these means all the requirements for the very highest 
power work are secured, and the very best condensers and highest power 
object-glasses can be successfully manipulated. 
“ Fram ” Microscope. — The “ Fram ” Microscope, recently brought 
out by Messrs. W. Watson and Sous, is illustrated in fig. 116. The 
object of this design is to produce a Microscope of the highest class at 
a very moderate price. The working parts are fitted and finished by 
hand, so as to obtain the smoothest and most precise action. The foot 
is of the tripod pattern with a spread of 7 in., and the instrument is 
absolutely steady in any working position. The coarse adjustment is 
Watson’s diagonal rack and pinicn, and the fine adjustment is the lever 
pattern applied to all the instruments manufactured by the firm, which 
has been tested for many years, and found satisfactory. One revolution 
of the milled head moves the body 1/300 in., thus giving very exact 
adjustment for high-power work, while the compensating screws pro- 
vide a remedy for any slackness that may arise after a long period 
of use. 
The coarse and fine adjustments are of the pattern adopted by 
Messrs. Watson in all their Microscopes. The stage, which is large, is 
of the Nelson horse-shoe shape, and the fittings are of the universal size 
throughout. The body with the draw-tube closed measures less than 
G in., and with the draw-tube extended 10 in.; it is therefore permissible 
to use objectives corrected for either the Continental or English tube- 
lengths. The lower end of the draw-tube is provided with the universal 
thread. In its plainest form the Microscope is provided with the ordi- 
nary tube fitting beneath the stage, to carry the condenser, &c., and is 
arranged to be turned aside from the optical axis when not required. 
This cau be replaced by a compound substage, fitted with rack and 
pinion focussing and screw centering adjustments. A sliding bar having 
a new form of spring fitting, affording a very smooth motion, has been 
designed for the instrument. The objectives are so mounted as to be 
approximately in focus when revolved on a nose-piece, and the eye-pieces 
are all arranged to work in the same focal plane. 
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