106 THE AMERICAN MONTHLY [Apr 
an inch, and the price, without mount, $20. We can re- 
commend this condenser for all high-power work, and it is 
of interest to remember that, so far as we are aware, 
Messrs. Swift & Son share with Messrs. Powell & Lealand 
the distinction of being the only makers of apo-chromatic 
condensers throughout the world. The second condenser 
is achromatic, and is an oil-immersion with a numerical 
aperture of 1.4 and an aplanatic cone that we estimate as 
exceeding 1:3. The corrections of this condenser are also 
excellent, and the working distance is ample, even witha 
thick slide. The power is about 4-inch, or #-inch with 
the front lens removed, and the price without mount is 
$19. Both condensers are constructed with the newer 
makes of glass manufactured in Jena. It says much for 
the enterprise, and the keen competition perhaps, of our 
English opticians that we should have been able to notice 
in these columns within a short period three different im- 
mersion condensers of high excellency by three leading 
makers. ‘ 
TARIFF EFFECTS.—American prices would scarcely serve 
for the English market, an apo-chromatic 1-12-inch oil- 
immersion objective of N.A. 1.3, for instance, being priced 
at-$120 — £24, and the corresponding objective of N.A. 
1.4 costing $160 — £32. Zeiss’ price for similar lenses 
are respectively £15 and £20. Thestands are built en- 
tirely upon the Continental model, which is closely ad- 
hered to, not only in the horse-shoe stand and in the fine 
adjustment, but also in the later Continental forms of sub- 
stage arrangements. 
THE ORDINARY CoLLopDION.—Flexile collodion is used 
medically and contains castor oil. We would recommend, 
however, Schering’s Colloidin, which is largely used by 
microscopists for section cutting. It can be obtained in 
chips or solution. A bottle containing 50 grams of the 
latter can be obtained from C. Baker for 30 cents. Beech- 
tar creosote is to be preferred, especially for cleaning col- 
