USING THE MICROSCOPE 
317 
ARTIFICIAL LIGHT 
During a considerable part of the year daylight is often insufficient 
for successful work with the microscope. Numerous contrivances 
for artificial illumination have been devised, some of them fairly 
good, but most of them thoroughly unsatisfactory. More than two 
hundred years ago Hooke used a device for artificial illumination 
which probably suggested the apparatus used by the late Professor 
Strasburger at Bonn. The apparatus in use in our own laboratory is 
only a slightly modified form of that used in the Bonn laboratory. 
The apparatus consists, essentially, of a hollow sphere filled with 
liquid. A fairly good and practical light can be got with an ordinary 
lamp by allowing the light to pass through a wash bottle filled with a 
weak solution of ammonia copper sulphate. A piece of dark paper 
with a circular hole in it serves as a diaphragm, and at the same time 
protects the eyes from the direct light of the lamp. 
At present, we.are using a white 50-watt, 115-volt, nitrogen Mazda 
bulb, with a shade to protect the eyes. This not only furnishes a 
strong light, without any glare, but throws a good light on the pencil, 
which is an important consideration in drawing with a camera lucida. 
Optical companies are now making excellent lights for microscopes. 
These lights furnish good illumination and most of them have the 
effect of good daylight. 
If laboratory tables are small, seating only one student, there 
should be a plug to attach the table to some convenient outlet; and 
also another outlet on the table for the microscope lamp. If the 
table is large, seating four or more students, there should be an 
outlet on the table for each student, and a single plug by which the 
whole table may be connected with a convenient outlet. 
For elementary classes, which are not likely to use higher powers 
than a 4 mm. objective with an ocular magnifying five or six times, 
individual lamps are not necessary in a well-lighted laboratory. 
Half-a-dozen strong lights, of the overhead type, with white shades, 
serve very well for a class of twenty-five or thirty students. 
