•journal D^^^^^^^^ I^SB of vavtous Microscopes. 
321 
V. — Mj/ Exjperienee in the Use of various Microscojpes. 
By Db. H. Hagen * 
Having worked with the microscope more than thirty years for 
medical and scientific purposes, — following the gradual perfecting of 
the instrument — I was anxious to examine the power of American 
microscopes. But my occupation in the Museum and ignorance of 
the English language have prevented the accomplishment of my 
wishes. I ordered a new microscope of M. Hartnack in Paris, 
which was kindly forwarded to me by M. Milne-Edwards. The 
French instruments are noted throughout Europe for their power 
and finish, and in order to judge impartially, I chose one of these, 
rather than a German instrument. It is well known that nearly 
every nation claims for itself the highest degree of perfection in 
the manufacture of microscopes. No Englishman would acknow- 
ledge the superiority of a French instrument, nor a Frenchman 
that of an English instrument. In Germany alone, Prussian, 
Austrian, 8axon, and Bavarian manufacturers all claim pre-emi- 
nence for their respective instruments, not only compared with each 
other, but with those of American and English manufacture. There 
to this question. I think these conflicting claims are based upon 
something beyond mere national pride. In fact, microscopes finished 
by the most skilful opticians, have arrived at a high degree of per- 
fection in nearly every country, and differ less than is generally 
supposed. During the past ten years there has been great compe- 
tition among opticians, but in every case their progress has been 
arrested by one insurmountable obstacle. Since the recent improve- 
ment in correcting the objectives for the thickness of the cover- 
glasses, comparatively little has been done. Indeed it is always 
stated and accepted as a fact, that the proper means of obtaining 
a stronger power consists in securing a higher power of the objec- 
tives and a smaller focal distance with greater angular aperture, 
and in this opticians have arrived at a rare degree of perfection. 
Objectives of ^^ih. in. are made, and the greatest angular aperture, 
so far as I know, is in the y^th objective by Spencer, with 175° 
angular aperture. But even here further progress is arrested. The 
increase of the angular aperture increases the two aberrations to be 
corrected, and materially weakens the penetrating power. Judging 
from an examination of the test-plate of Nobert, it would appear 
that the best instruments of any country differ but little in power. 
It was stated, at a recent meeting, that Messrs. Stodder and Green- 
* The following paper was read before the Boston Society of Natural Science 
on the 10th of March last. We reproduce it because it contains an interesting 
sketch of the qualities of different instruments not generally familiar to English 
workers. — Ed. M. M. J. 
VOL. II. z 
has been no unanimity of 
scientific men in regard 
