120 MICROSCOPY. 
z 
Here we have a gentleman, well known throughout the micros 
cal world as one of the most accomplished theoretic opticians 
London, generally supposed to be the principal advisor of 
working opticians, not apologizing for, but practically defen 
the imposition, one that bas been exposed and complained of 
Dr. Wm. B. Carpenter * and also by a writer in the “Qua 
Journal of Microscopical Science.” 
Mr. Wenham says “a scientific microscopist gives the diam 
with his illustrations and the nominal power of his object g 
this quite meets the case.” In this Mr. Wenham is entirely wr 
it does not meet the case. A power of one-thousand diam 
obtained with a one-inch objective is a very different thing 
one-thousand diameters obtained with a one-tenth, wnless the $ 
inch is ten times as good an instrument as the one-tenth. The S 
entific microscopist should g’ve with his i 1-strations, not 0 
amplification he employed, but the real focus of the oh 
and the name of the maker, as astronomers do in the case 
telescopic observations. 
He farther says, “in such a difficult and complex arrangt 
as a high power object-glass, it is almost impossible for all 
makers to work to the same magnifying standard.” 
course depends on the knowledge of opties possessed by the 7 
man, but has nothing to do with the matter. When the objec 
is made, the focus can be measured, and the glass named 
ingly. The nearer the actual power comes to that inten 
much the more credit to the maker — the farther it is from 
he sells it for the more to his discredit. It is an axiom ae 
copy that the lower the power of a glass that will give 
. result or effect, the better the glass. e 
< Mr. Wenham’s comparison with the steam engine IS as 
propriate as Hartnack’s objection to English micros¢ 
_ With their wheels and screws they look like a steam engine. 
sae 
_ PHOTOGRAPHIC MICROMETER AND GONIOMETER. — I : 
_ worth, of Georgetown, D. C., proposes, in the “ Americal 
_ of Science and Arts,” a photographic positive on glass 
stitute for the ruled micrometers. Lines of one-sixth inch 
~ are reduced by photography to ; 3 inch, mounted 1n > 
~ used like the ordinary eye-piece micrometers. The lines 
_ *The Microscope, ete. London. 1868. p. 184. 
