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PROCEEDINGS OF SOCIETIES. 
as to flatness and clearness of field, definition, amplification, and reso- 
lution ; its angle of aperture is wonderful, wliile its achromatism 
and even its penetration are very fair, and its working focus sufficient. 
From the observation noted above we deduce one very important 
fact, viz. that the different appearances of lines, dots, hexagons, 
&c., on Pleurosigma angulatum are not only the varied results of 
angle of aperture, of amplification, and of illumination, but that 
they may be obtained with less and less obliquity of light as we 
increase the power of the objective ; thus making it evident that high 
powers with direct central light show us clearly things which we 
rather guessed at than saw (owing to the increased chance of spherical 
and chromatic aberration and distortion from the employment of 
oblique light) with lower ones. 
We would conclude, therefore, by recommending these high-power 
lenses to those engaged in microscopic research, not as capable of 
doing all work— a 1-inch is as indispensable to a histologist as a 
^th — but as likely to be proportionately useful in unravelling the 
mysteries of organic life. 
Dr. J. Gibbons Hunt desired it to be distinctly understood that 
he had nothing to do with the preparation of the report, and did not 
wish to be held responsible as a member of the committee for the 
views advanced in it. He considered that it embodied the obsolete 
views of Carpenter and Beale in regard to penetration, which term 
should be dropped from the vocabulary of microscopists. He believed 
that penetration and resolution can be and have been combined in the 
best objectives. 
Dr. J. Cheston Morris stated that the report was based upon a 
careful and conscientious examination of the objectives by the com- 
mittee, and was in accordance with the well-known laws of reflexion 
and refraction of light. He had submitted the report to Professor 
George F. Barker (of the University of Pennsylvania), who had 
approved it so far as the optical questions were concerned, except, 
perhaps, on the subject of penetration, which he attributed to imper- 
fect spherical correction. He could have wished that Dr. Hunt had 
expressed his dissent from the document as freely in private, when it 
was shown to him, as he had just done. All he did at that time was 
to suggest some slight alterations and additions, which being made, 
Dr. Morris was led to expect his adhesion to the report. As to the 
question of penetration being a useless one, he considered the pre- 
sence of this quality in the lenses of ToUes of great moment. High 
angle of aperture and penetration have not been combined in the ob- 
jectives of the German, English, and French makers to the same degree. • 
Dr. Hunt said that what one man calls penetration another does 
not, terms often being used without an exact knowledge of the mean- 
ing intended to be conveyed by them. He preferred a lens that will 
give one absolute focus rather than three indistinct ones. The con- 
ditions of testing are frequently fallacious, and imperfect illumination 
is one of the most prolific sources of error. With low objectives, as, 
for example, a |th, used with the amplifier, very satisfactory and 
reliable results can bo obtained. 
In conclusion, Dr. Hunt proposed that at some time during the 
