60 MICROSCOPY. 
ment in the construction and study of objectives, and intimates, i 
which is hardly saying too much, that the peculiar qualities of the E 
objectives depend more on their angular aperture than on their | 
focal lengths. “Focus and aperture are in fact both essential 
factors in the denomination of an object-glass, and where a differ- 
ence exists in either we must keep in mind that we are comparing : 
different things, and not the same things with differing qualities.” 
The estimation of any angular aperture, so well expressed by “Bie 
is perfectly familiar and undisputed among experienced microscop- 
ists, although its exact bearings are not always easily apprehended 
by beginners ; and that microscopists need occasional caution 1m 
regard to it may be inferred from the case in point, where an a 
complished writer stated an extraordinary performance of à lens 
without mentioning the range of its apertures or the aperture be : 
which he worked it. The peculiar and entirely independent quali- 
ties of lenses of low and of high angles are everywhere understood 
alike ; but the extent to which success has been attained`in this 
country in the construction of high angles cannot be appreciated a 
abroad when “B,” evidently well informed on other points, woul p 
_not be surprised to hear that a one-fifth of excessive resolving 
power had an angular aperture of 150° or 160°. Any onein ki : 
country would be *‘ surprised” to hear that its highest angle bic! 
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Makers should always engrave the angular aperture upon t a 
mounting and on the boxes of their objectives. The neatness and a 
sufficiency of this plan, however, is marred in the case of many, = 
modern objectives whose screw-collar adjustment gives a WW | 
range of powers and angles. Exactly at what point of adjustment 
the measurements should be made in these cases is one of the mo 1 
difficult points to be settled in endeavoring to obtain a unifor i 
nomenclature in regard to the works of different makers. At least Í 
for the present, until some standard degree of adjustment can be 
agreed upon, both the highest and lowest figures should be gv 
where the range is considerable. : ae 
PASSAGE or CORPUSCLES THROUGH THE Broop-vessers. — The” 
‘t Monthly Microscopical Journal” reviews a paper on the subject 
read before the Royal Society by Dr. R. Norris. Previous hy 
potheses fall short in regard to the most singular and im ; : 
part of the process. ‘The question is less how the corpuscles 8°" — 
