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NOTES AND MEMOEANDA. 
Angular Aperture of no Importance ! ! !— An American gentleman, 
who certainly speaks, if with no other favourable quality, at least 
with firmness and decisiveness, has read a paper on the above ques- 
tion before a recent meeting (Jan. 5, 1875) of the Memphis Micro- 
scopical Society. The following extracts from his communication 
will be read with some little surprise : " Now, gentlemen, it is with 
some diffidence, but with no lack of firmness, that I assure you there 
are a few of us who have been hard workers at the tube, who do not 
believe this doctrine of penetration, and did not believe it ten years 
ago. To my mind a good object-glass, whether of low or wide aper- 
ture, should give intense definition on one focal plane and one only ; 
any variation from this (penetration or what not) will be at a sacrifice 
of the intensity of the definition. The modern objectives of to-day 
(1874) as furnished by our countryman, Mr. ToUes, having air angles 
of 180°, and balsam angles of, say, 85° to 95°, are instruments in 
every respect far removed from the objectives of ten years ago ; these 
glasses admitting both the central and oblique pencils almost per- 
fectly corrected, and thoroughly under the control of the eminent 
optician who has just introduced these new 'four systems/ — hence 
they work equally well either by central, moderately oblique, or very 
oblique light, and are equally serviceable for the purposes of histolo- 
gist or diatomist. Now for the proof. Select any object (only be 
sure and not select a diatom, for Dr. Beale says that such look con- 
fused when received with low-angled glasses) : suppose you take a 
blood-corpuscle or a specimen of striated muscular fibre, or any- 
thing you may elect ; view this, using central light with the new four- 
system ToUes' yV^h, recently purchased by your secretary, Mr. Dod, 
first with A, afterward with B, and other still higher eye-pieces, thus 
carrying the amplification up to 7000 diameters or more, and note 
what you see. Now remove the ToUes', substitute the best low-angle 
objective that can be obtained, repeating the previous experiment. 
Assuming that both objectives are manipulated so as to obtain maxi- 
mum performance of each, I confidently predict that the ToUes' J^tb 
will vastly excel any low-angled objective extant. The view of your 
object, as seen with the ToUes' yVth, under an amplification of seven 
to eight thousand diameters, will be sharply defined and well illu- 
minated, while with the low-angle glass you will do well to see the 
object thus amplified at all. I shall be greatly pleased to have the 
Society try this and similar experiments, and feel sure that the re- 
sults obtained will surely explode the current idea that wide-angle 
glasses are of no use to the histologist. At a future time I shall 
offer further remarks, and will give in detail a few experiments of 
mine which perhaps some of your members will be sufficiently in- 
terested in to repeat." 
