110 THE AMERICAN MONTHLY [ June, 
ing the stage, passed merely from an orange-purple to a dull gray. On 
introducing the cap and passing diaphragm from right to left a beautiful 
series of the most brilliant tints was seen—a fine navy blue changing to pur- 
ple, orange, and then to lemon yellow, and lastly pale straw color. 
A section of fortification agate was taken which showed a small crystal of 
pure quartz in one portion. With the diaphragm used as before from right 
to left the color of the crystal was merged from bright green to magenta and 
then to a velvety brown-red. With the usual revolution of the stage the col- 
ors exhibited were green fading to a dull black. 
With this apparatus there is not only a more varied and brilliant series of 
colors, but also a marked intensification of points of structure. In the two 
above mentioned slides delicate lines of crystallization were shown which 
were invisible under ordinary circumstances. 
One of the small, curiously branched bones of the Red-horse, a fish com- 
mon in this region, was examined and showed the bone cells in a remark- 
ably distinct way, they being quite indistinct without the diaphragm. 
Ryder’s Automatic Microtome.*—This new instrument has been 
devised by Professor John A. Ryder, of the University of Pennsylvania, in 
order to facilitate the preparation of sections for large classes, and also for the 
rapid preparation of series of sections in ribbons in embryological work, in 
which the element of time becomes a serious consideration. The device 
is small and compact, and is also automatic—that is, the same movement 
which cuts the section also brings the block into position for cutting the 
next successive section, and so on continuously, of any desired uniform thick- 
ness; the cutting takes place as fast as it is possible to move a vibrating lever 
up and down through a distance of three inches with the right hand. 
The working parts are an oscillating lever, which is provided with a clamp 
at one end, into which the paraffine-holders are adjusted, and at the other with 
a simple handle. This lever rests upon trunnions on either side, and these 
in turn rest in triangular notches at the top of the two pillars between which 
the lever oscillates. At the cutting end of the lever a spring pulls the lever 
down and effects the sectioning and also the adjustment for the next section. 
The lever is pushed over and adjusted for the successive sections by a hollow 
screw, through which passes the trunnion on the side away from the knife. 
This screw is fixed to a toothed wheel, three inches in diameter, which re- 
volves close by the side of the oscillating lever. The toothed wheel and screw 
is actuated by a pawl fixed to the side of the lever near the handle. The 
number of teeth which this pawl can pass in a single vibration downward is 
controlled by a fixed stop screwed into the under side of the oscillating lever 
near the handle; the end of this stop striking on the top of the bed-plate thus 
brings the lever to rest at a constant point in its downward excursion. An 
adjustable sector by the side of the toothed wheel throws the pawl out of gear 
after a given radius of the wheel has been turned through an arc embracing 
the desired number of teeth. This adjustment is also effected before the block 
containing the object to be cut reaches the edge of the knife. The adjust- 
ment for the next section is therefore effected while the surface of the block 
is not in contact with the under side of the knife, so that no flattening or scrap- 
ing effect is produced on the surface of the block in its upward passage past 
the knife. 
The movement of the vibrating lever being arrested at each down stroke 
*From the American Naturalist, March, 1887. We are indebted to Mr. Joseph Zentmayer for the illustra- 
tions of the instrument. 
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