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NOTES AND MEMOEANDA. 
An American ¥iew of the recently expressed opinion, as to 
Objectives, of tlie Academy of Matnral Sciences of Philadelphia. — 
The following letter was addressed to the editor of the ' Cincinnati 
Medical News ' (June, 1875) by Mr. J. E. Smith :— " In your last 
(May) number of the News I notice the report ' of the committee 
appointed to examine optically the ^^th. and -^Qth objectives displayed ' 
at the late exhibition of the Biological and Microscopical Section of 
the Academy of Natural Sciences of Philadelphia. 
" According to this report it seems that of the six objectives 
tested (?) a ToUes' wet ^V^h of 140° and a Wales' ^\th of 170° were 
the only glasses that displayed the hexagons (?) of P. angulatum by 
central light. 
" A few months since, a correspondent of the London Micro- 
scopical Journal proposed using P. angulatum with central light from 
an ordinary candle, as a test for objectives of medium power. I at 
once repeated his experiment, using a ^th and yV^^ four-system 
immersion glasses, made by R. B. Tolles, and was simply amused at 
the result, to wit : the hexagons were instantly displayed with either 
objective, using a common tallow candle for illumination — the angle 
of obliquity 0 ! 
" A friend of mine, a well-known ' expert,' who had just purchased 
a Tolles' four-system yo^^? ^^^^ article in the London Journal, 
advised me that he too repeated the experiments, and with the same 
results as I obtained with my \ih. and yoth. 
" The ' committee appointed to examine optically, &c.,' having 
obtained the above-stated curious results, to wit : that the g^th and 
the 23-^^ were the only glasses that would display the Angulatum 
hexagons by central light, proceed to deduce one very importoMt fact ' 
(italics mine), viz. that the different appearances of lines, dots, 
hexagons, &c., on P. 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 ive increase the 
power of the objective (italics mine again), 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 employ- 
ment of oblique light) with lower ones. (!) 
" The committee therefore conclude by recommending these higher 
power lenses to those engaged in microscopic research, &c. 
" This was too much for Dr. Hunt to stand. The Doctor desired it 
to be distinctly understood that he had nothing to do with the prepara- 
tion of the report, and did not wish to be held responsible as a 
member of the committee for the views advanced in it. Dr. Hunt 
considered that it embodied the obsolete views of Carpenter and Beale 
in regard to penetration, which term, he says, should be dropped from 
the vocabulary of microscopists. ' He believed that penetration and 
resolution can be and have been combined in the best objectives.' 
