58 
ACCESSORY APPARATUS. 
tance for easy and accurate drawing. The size of the picture 
will vary with the distance of the paper from the instrument. 
Experience is of course required to give steadiness to the 
hand and to secure accurate drawings, but it is often so desira- 
ble to make accurate drawings of objects seen with the micro- 
scope, that every one ought to practice till he can draw with 
facility. It makes little difference which of the three instru- 
ments described is used, a person draws best with the instru- 
ment to which he has become accustomed. 
78. Camera I^acida applied to Micrometry. If the 
microscope is placed at an angle convenient for using the 
camera, and care is taken to adjust it always in the same posi- 
tion, the lines on a stage micrometer may be projected on 
paper, by means of the camera, and form an accurate scale 
for measuring any object drawn with the same power, and 
with the instrument in the same position. Supposing the 
divisions of a stage micrometer, whose real values are 2 J 0 
an inch, are projected with such a magnifying power as to 
be at the distance of one inch from each other on the paper, 
it is obvious that if any object is delineated on the paper with 
the same power, every inch of the drawing corresponds to 
2^5 of an inch on the object, J of an inch would equal one 
thousandth of an inch in the object, and so on. We may there- 
fore draw parallel lines on the paper, subdividing the spaces 
formed by projecting the micrometer lines, and the scale thus 
formed will serve for measuring any object we may examine. 
A similar scale may be prepared with each object-glass, and 
by viewing any object through the camera, with the scale 
placed below, we determine at once its magnitude. When 
sufficient magnifying power is used, the instrument properly 
adjusted, and the scale thus made is minutely divided, great 
accuracy may be obtained. 
79. Movable Hiaphrag^m-Platc. “ ISTo microscope stage 
(says Dr. Carpenter) should ever be without a diaphragm- 
plate, fitted to its under surface, for the sake of restricting the 
amount of light reflected from the mirror, and of limiting the 
angle at which its rays impinge on the object.” This appa- 
ratus, shown at Fig. 27, is attached to the under side of the 
J. & W. GRUNOW & GO’S ILLUSTRATED 
