10.]
§2. Sclerotica and Cornea
11
to tenths of a degree. Inside the box, each axle carries a toothed wheel ee
and a metal frame g in which the glass plate / is fastened. The frame of each
plate has only three sides, the side turned towards the other glass plate being
missing. The two glass plates constituted originally a single plane parallel
*/
Fig. 4.
plate. A complete metal frame was made for this plate and fastened between
the surfaces of the two toothed wheels. Then the axles were rounded off on a
lathe and finally the frame was cut through in the middle. The glass plate
was cut through in the same manner, and each half fastened in its correspond¬
ing half of the frame. Thus an exact adjustment of the positions of the plates
on the two axles was accomplished. The toothed wheels are moved by the
sprockets C\ and c2 which are rigidly connected with the axles biCi and &2c2.
Moreover, each of these axles has a
sprocket h in the middle. If the
knob at b\ is turned, the lower
toothed wheel controlling the lower
glass plate will be moved by means
of the sprocket C\. Furthermore,
the sprocket hi engages with the
sprocket h2 and rotates the second
axle b2c2 by an equal amount in the
opposite direction. As a result of
this the sprocket c2 acts upon the
upper toothed wheel connected with
the upper glass plate and turns it
through an angle almost as large
Fig. 5.
__ w w that of the lower plate. The rota¬
tion of each plate is measured by the graduated discs attached to the axles
on the outside of the box.
as