Dre Tuer MiIcRoscopr. 
scopists must have short body-tubes, and not only lose consider- 
ably more than they gain, but also injure ignorant beginners 
who go to them for advice, and are sent to Europe for stands 
made after the continental model. In this country, except 
among a few, these short body-tubes are not favored. Yet many 
manutacturers place them on their stands, supplying also a draw- 
tube which is really a part of the body, since it must be pulled 
out to obtain a body of the standard length, the draw-tube in 
reality being absent. 
The magnifying power of the combined eye-piece and objective 
may be lessened by shortening the body, and greatly increased 
by lengthening it, so that it would seem an advantage if a lower 
power could be obtained by the short body, and a higher power 
by drawing out the tube to the standard length, the same ob- 
jective being used in both cases. It would seem that as much 
could be obtained in this way from one objective as from two 
used on a standard body. To a certain extent this is true. 
With bodies of the standard length, in which a draw-tube will 
generally be found, the power may be enormously increased by 
the use of the draw-tube, yet the result is anything but desirable 
or praiseworthy. The standard body, however, cannot be 
shortened, yet in many instruments, always in the best ones, 
there is a diaphragm within the body to which very low power 
objectives may be attached, and a very low magnifying power 
thus obtained, Even here, however, the result is gratifying only 
in objectives of very low power, and the reason for it is the same 
that holds good in the attempt to obtain two or more degrees of 
amplification from the same objective by the use of a short 
body lengthened by drawing out the tube to the standard. 
There are several kinds of objectives, but the two great divis- 
ions, into one of which all must be classed, are adjustable and 
non-adjustable. That is, for certain optical reasons, the adjust- 
able objectives are supplied with a rotating collar which, when 
turned moves a part of the compound lens, the position of the 
other parts remaining unchanged. This affects for the better 
the appearance of the image, and is always present on the best 
objectives, except on some of the apochromatics of Zeiss, where 
it ought to be. In the non-adjustable objectives the lenses com- 
posing them are immovable, being firmly fastened to the brass 
mounting by the optician. These are not so valuable in an 
