Tue MIcROScOPE. 301 
is without exception. It is that any body tube with a screw on 
its lower end of a diameter less than three-fourths of an inch 
should be rejected without a moment’s hesitation. And con- 
versely, any objective with a screw on its upper end of a diam- 
eter less than three-fourths of an inch should be rejected even 
more speedily. Any stand or any objective without the Society 
screw may safely be set down as a good thing to be avoid- 
ed, and the reader may also justly view with suspicion any 
objective which must have an adapter to fit it to the Society 
screw of the stand. All of our American opticians are good 
and true men, but their wares are for sale, and they have a right 
to live up to the principle of caveat emptor in their business deal- 
ings. These gentlemen have “French Triplets” for sale, and 
any ignorant beginner will be allowed to buy 
them if he wants them. But I would advise 
him not to want them. These abominations === 
in the way of objectives are, as expressed by a 
bit of unrefined yet expressive English slang, 
“cheap but nasty.” And every one of them 
has a screw smaller in diameter than the joie ee 
Society screw, and every stand prepared to SS 
receive them has the same defect. 
In figure 1 is shown, about natural size, a ofo 
first class adjustable objective. It is repre- ARMREST ANGEES: 
sented as standing on its screw end, as al? 
objectives should be placed when not on the 
instrument or in the brass eylimdrical box 
which always accompanies them. This Fig. 1. 
lower end, as it seems to be in the figure, 
really the upper end as it is applied to the 
stand, bears the Society screw. The narrow 
oblique portion graduated to degrees by the 
short straight lines engraved upon it, is the 
movable adjustment collar which is rotated by 
turning the milled ring next above it, and 
separated from it by the short cylindrical 
Fig. 2. portion of the brass mounting. The upper- 
most end of the succeeding cylindrical part bears the glass lenses 
composing tne optical portion of the objective, the entire brass 
tube being the mounting and intended to carry and protect the 
