THe Microscope. -) 209 
now occupies a position which is second to none. The student in 
every department of science must now be familiar with the micro- 
scope. Truly did Schleiden, a most successful investigator, say : 
“He who expects to become a botanist or a geologist without using 
the microscope, is, to say the least of him, as great a fool as he 
who wishes to study the heavens without a telescope. ” 
Tue Usr oF THE Camera Lucrpa.—In most cases when a mi- 
croscopic image is to be traced, recourse will be had to some 
camera lucida. The use of this very helpful apparatus is very 
soon and very easily learned. There is therefore need of saying but 
very few words about it 
The eye should be held close to the opening, provided for see- 
ing in the instrument and look perpendicularly down, for by look- 
ing obliquely the image may be considerably distorted. The paper 
upon which the drawing is to be made should be fastened lying 
flat at a standard distance of 25.4 cm. from the camera lucida. It 
is best to provide a drawing board upon which the paper may be 
fastened and which may be placed at this distance from the ca- 
mera. 
In order to draw a picture by means of the camera lucida 
without painfully straining the eyes, it is necessary that the micro- 
scopic image, and the paper and pencil be uniformly illuminated. 
If the image has, in comparison with the paper too strong a light 
the pencil will be seen with difficulty if at all. On the contrary, if 
the paper in comparison to the image be too strongly illuminated, 
the delicate outlines of the latter will be indistinct. The first 
usually occurs where the image of the paper and pencil is thrown 
into the field of view of the microscope and the latter when the 
microscopic image is reflected upon the paper. This difficulty 
may be remedied by throwing either the image or the paper into a 
shadow. Both may be done simply with the hand, or by a prop- 
erly constructed screen of paper, or by a disk of pasteboard set up 
at some distance, and the like. A few trials with the microscope 
with different magnifications will afford the necessary experience 
for properly managing the light. In tracing the outlines of the 
image under the camera, the pencil used should not be too hard 
and the lines should be very light, and then they will afterward ap- 
pear rough, for the position one has to take in this work is not very 
favorable to nice drawing.— Behrens, 
