270 THE MICROSCOPE. 
supporting the whole instrument above the pillars. In the 
anatomy of the stand the arm is therefore one of the most im- 
portant members. 
THE BODY. 
I do not suppose that even the most economical manufacturer 
has ever thought of forming a microscope body of sheet iron. 
The material is always brass. In a single instance only, so far 
as I know, an entire stand has been made of silver. This was 
done by Messrs. R. & J. Beck, of London, for a gentleman in 
New Orleans. Like diamond lenses, silver stands are for the 
few, and probably only the minority would care for them. 
Modern objectives of glass are far superior to objectives of dia- 
mond, and silver as a material for a stand is about as undesir- 
able as can be imagined. Sheet iron would probably be more 
serviceable. 
No manufacturer makes the body of a length and diameter 
equal to the length and diameter of the body-tube of any other 
manufacturer; and some makers have as many as three sizes, so 
far at least as regards the diameter, while the variation in Jength 
is almost as great. This gives trouble when it is desired to use 
the eye-pieces of one optician on the stands of another, and 
necessitates a special fitting for the eye-pieces, unless the pur- 
chaser is willing to use those accompanying his stand, as he 
usually is until he wants a “solid,” a “ periscopic,” or some other 
variety. Then, if the tube is too large, the eye-piece must have 
an adapter of brass applied by the dealer, to prevent it from fit- 
ting too loosely and from slipping to one side when the micro- 
scope is inclined, and from thus falling too far from the optic 
centre; or it must: be wound around with paper, a device that I 
have tried successfully more than once. But if the tube is too 
small to receive the eye-piece, the microscopist begins to appre- 
ciate the trouble of non-uniformity in the size of all eye-pieces 
and of all body-tubes. . The desirability of this uniformity has 
long been recognized, and the American Society of Microscopists 
has distinguished itself by its continued efforts to accomplish 
the change from this variety of sizes to one standard. . The 
attempts and recommendstions have been toward a standard 
size for the eye-piece particularly, which of course necessitates a 
uniform diameter of the body-tube. This uniformity, however, 
will never come until the clamor of purchasers forces the dealers 
