Tue MIcROoscoPe. 303 
in its optical results, or with those parts separated for lower 
powers, the lenses unscrewing from each other, when the results 
are, if possible, even more abominable. When the triple com- 
bination is separated into its three parts, each brass mounting is 
just one-half inch in diameter, while the glass lens measures 
one-fifth inch across, and the aperture of the screw one-fourth 
inch. The special instrument from whose French Triplet these 
measurements were made, had its screw about one-fourth inch 
in diameter, of course, but the actual size of the round hole 
through which the light was admitted into the body after hav- 
ing passed through the objective, was one-tenth inch! Carefully 
— reject all so-called objectives of these dimensions. 
Each part of the three lenses forming the French Triplets is a 
thin brass disk, an opening on the upper side being encircled by 
the screw thread, while the lower surfave bears a circular, pro- 
jecting ring into which the single plano-convex lens is fastened, 
the ring having an external screw thread. In good objectives, 
even the most inferior produced by any reputable maker, cor- 
rections are made for spherical and chromatic abberation. In 
French Triplets, however, no attempt at correction is made ex- 
cept by the superposition of the two or three simple plano-con- 
vex lenses forming the combination, the one below being sup- 
posably corrected by those above. Yet at the present day, when 
the cheapest American objectives are infinitely superior to the 
most expensive French Triplets, the latter are kept in stock by 
the dealers, and sold when demanded. 
The Triplets are the highest powers of those optical abomin- 
ations. The low-powers are in another form. These are called 
Doublets or often “Stove-pipes.” They consist of a blackened 
brass cylinder one-fourth inch in diameter and one-half inch or 
less in length, to each end of which is screwed a single plano- 
convex lens, the whole Stove-pipe being applied to the body tube 
when the abomination is to ke used. Stove-pipes are no better 
corrected and no more desirable as objectives than the Triplets. 
Yet in one sense they are cheaper, while in another they are 
more than costly. A Doublet with one inch focus costs two 
dollars and one-half, and even at that price its expensiveness is 
phenomenal. A one-fifteenth inch Triplet, a high power, can 
be had for ten dollars, and is worthless for anything but a toy. 
As these objectives are supposed to be employed either combined 
