188 NATURAL HISTORY MISCELLANY. 
the best American glasses, and the best of Hartnack’s, Gundlach’s 
and others; the glasses being mounted similarly, with private 
marks only for recognition, so as to prevent all possibility of 
prejudice on the part of the committee. Were this done, the re- 
sult, whichever way it tended, would be eminently satisfactory. 
Of this the writer is sure, that many persons—even eminent 
microscopists—have made up their minds about the qualities of 
_ foreign objectives, without having seen any, or only very poor ex- ` 
amples, and then when a really fair specimen of such a glass is 
placed before them, they exclaim with astonishment “ Why this is 
the finest glass I have ever seen.” We shall be glad to receive 
Suggestions or assistance, in carrying out the proposed comparison 
of objectives. Dr. Royston Pigott has expressed his willingness 
to aid in such an undertaking. — E. R. L., in Nature. 
CÓMMITTEE FOR Testine Opsectives.— Dr. G. W. Royston 
Pigott proposes (Monthly Microscopical Journal, London, March, 
1871) the appointment of a committee for the examination and 
comparison of objectives by different makers. Both dry and im- 
mersion lenses should be tested ; and, to avoid prejudice, they 
should all be mounted in a uniform and simple style, marked in 
cipher, and identified as the work of known makers only after the 
final report of the committee. They should be tested in reference 
to the following properties :— Resolution, Penetration, Magnifying 
power, Spherical and Chromatic aberration, and Angular aperture. 
Dr. Pigott also judges that “ deep” eye-pieces should be employed, — 
and a very limited and unusual illumination, points which might be 
left to the judgment of the committee, who would probably prefer 
to use all kinds of eye-pieces and various methods of illumination, a 
not forgetting, of course, the separate testing of the different parts 
of the same objective, by the methods lately introduced by Dr 
Pigott. (The writer has excellent lenses by the best makers; 
in which not only are the different zones of angular aperture une- 
qually corrected, probably a more or less unavoidable error, but 
also the correction is distinctly unequal [from imperfect center- — l 
ing?] at equal distances from the axis; a pencil, say, at 40° from 
the axis, being better corrected than one at the same distance 02 
the other side of the axis.) í 
As this subject is largely an international one, though not % 
sufficient importance to call for the meeting of a committee repre! - 
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