CHAPTER XXVI 
USING THE MICROSCOPE 
The investigator who desires to see all that his microscope is 
capable of showing must study the optics of his instrument. The 
fundamental principles are presented in any good textbook of physics. 
Excellent practical hints are given in two booklets published by the 
leading American optical companies. These booklets tell the begin¬ 
ner how to set up the microscope, how to keep it in order, and give 
directions concerning illumination, dry and immersion objectives, 
mirror, condenser, diaphragm, and various other things (Fig. 115). 
They were doubtless written for advertising purposes, but since they 
advertise by giving directions for securing the best results with the 
microscope, the information is very reliable. The Spencer Lens Com¬ 
pany of Buffalo, New York, and the Bausch & Lomb Optical Company, 
of Rochester, New York, furnish these booklets free of charge. 
In the histological laboratory where preparations are being made 
the microscope is in constant danger. A cheap microscope with a 
16-mm. objective and one ocular, such an instrument as can be got 
new for $30 or less, can be used for examining preparations while they 
are wet with alcohols, oils, or other reagents. If it is necessary to use 
a better instrument for such work, cover the stage with a piece of 
glass—an old lantern slide is of about the right size—and be extremely 
careful not to get reagents upon the brass portions. 
MICROMETRY 
Everyone who expects to become at all proficient in the use of 
the microscope should learn to measure microscopic objects and 
should learn to form some estimate even without measuring, just 
as one guesses at the size of larger objects. In any measurement 
one should note the tube length, which is usually 160 mm. Since 
the use of the nosepiece is universal, it is convenient to have the 
length measure 160 mm. when the tube is pushed in. Some com¬ 
panies still make the tube so short that it must be pulled out about 
15 mm. to reach the length of 160 mm., even when the nosepiece is 
in place. Where there is no revolving nosepiece, the draw-tube 
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