UNIFORMITY OF NOMENCLATURE IN OBJECTIVES. 143 
* in., and }in., giving powers of 5, 74, 10, 15, 20, 30, and 40 
diameters. The writer has applied the same names to his oculars, 
applying the intermediate fractions 55; in., žin., and }in., to inter- 
mediate powers; and he is satisfied, by experience of its con- 
venience, that this nomenclature only needs a trial, to secure its 
adoption by all who use the microscope for other purposes than 
amusement. Of course any microscopist, having determined the 
power of an objective and the powers of the microscope when that 
objective is used with his various oculars, can obtain the powers 
of his oculars by dividing the latter numbers by the one first named, 
and can then name his oculars, like the objectives, either by their 
magnifying powers or by their equivalent focal lengths. The 
rivalry of makers and the interests of trade are not involved in 
this case as in that of the objectives, and there may be no reason 
why this plan,if as acceptable to microscopists generally, as it has 
been to a few, should not come into immediate use. 
In order to work the objectives and oculars at their standard 
powers they should be of course, about ten inches apart either by 
length of compound body or by use of draw tube ; and it is believed 
that most objectives whose corrections are accurate enough to show 
any difference will work best at about this distance. Should a 
decidedly different distance be used in any observations of impor- 
tance, it would be well to state that fact in recording the observa- 
tion. 
In reviewing this subject, the following points would seem to be 
reasonably well settled. Objectives should be, and could be toa 
much greater extent than they now are, rated according to a uni- 
form standard. They should be named not arbitrarily, but in a 
manner indicative of their magnifying power. Ten inches is the 
standard distance of measurement in estimating powers. This dis- 
tance should be taken from the eye to the rule by which the meas- 
urements are made, without regard to. the distance of the object 
on the stage. Magnifying power is always stated in linear meas- 
ure. The magnifying power and angular aperture, as well as the 
maker’s name, should be engraved on all objectives, and added to 
all particularly important drawings made by their means. Ocu- 
lars Should be named, like the objectives, in such manner as to 
indicate their magnifying powers or equivalent focal lengths. 
The following are some of the more important queries which still 
remain open. Should the standard one-inch objective be charac- 
4 
