ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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The instrument is fitted with a new centering substage, having both coarse 
and fine adjustments ; so that when using high powers with the Abbe 
condenser, the most accurate focus can be obtained with the least amount 
of trouble. 
Bausch and Lomb’s Continental (Grand Model) Microscope. — The 
large body- tube of this instrument (fig. 78), especially constructed to 
permit a large cone of light to pass from the objective, fits this stand 
especially for photomicrography. The base, of horse- shoe type, is extra 
heavy, and has the back claw prolonged so as virtually to form a tripod 
base, which is entirely stable in any position of the Microscope. The 
stage is of unusually large size, measuring 126 mm. in diameter, and is 
fitted either with a vulcanite plate or a mechanical stage ; in either case 
the stage is revolving, and with centering screws, whereby the geo- 
metrical centre of the stage may be made to coincide accurately with 
the optical axis of the objective. The heads of the centering screws 
are provided with graduations and index, and with a series of lines 
recording the number of revolutions of the screw. It is claimed that 
these extra graduations make this the only Microscope provided with 
revolving mechanical stage, with which it is possible to record accurately 
the position of any given object, in such a manner that it can be referred 
to again if the instrument shall have been used ad interim for other 
work. The mechanical stage is readily interchangeable with the plain 
revolving stage. To effect the change, it is merely necessary to loosen 
the centering screws and substitute one stage for another. 
The fine adjustment is an improved triangular bar adjustment ; and 
in order to give increased delicacy in manipulation, the head of the 
micrometer screw is made extra large, and has a concavity at the apex 
in which to rest the index finger for greater steadiness. The circum- 
ference is graduated to 100 parts, permitting measurement of the thick- 
ness of objects under observation. 
The coarse adjustment is by diagonal rack-and-pinion, the advantage 
of the diagonal teeth being that much greater delicacy of movement is 
secured, together with greater lasting qualities, as three teeth engage at 
all times, and with a shearing contact, instead of in the jarring fashion as 
with the straight rack. The sleeve carrying the draw-tube is removable 
when using the stand for photography. 
American Type Microscope. — Fig. 79 represents Messrs. Bausch 
and Lomb’s “ Universal ” pattern of this instrument. A large bronze 
pillar, jointed for inclination, is fitted on a brass trijpod base, and a heavy 
thumb-screw (not shown in the figure) secures the instrument in any 
desired position. The coarse adjustment is by diagonal rack-and-pinion 
of long range. The fine adjustment is by micrometer screw, working in 
a steel nut on the triangular bearing of the arm. The head of the micro- 
meter screw, silvered and graduated, is provided with an indicator. The 
main tube has two graduated draw-tubes sliding in the cloth-lined main 
tube. The stage has concentric revolving motion and removable spring 
clips. The large-sized mirrors are plane and concave ; both these and 
the substage with its dome diaphragm are separately adjustable on their 
respective bases; the circular bearings of these are large, and are 
graduated to degrees and silvered. Mirrors and substage bars have 
