Monthly Microscopical 1 
Journal, March 1, 1869. J 
COBRESPONDENCE. 
199 
and now, after four months, it comes before tlie Fellows in your last 
issue, but modified and altered almost beyond recognition, as tbe 
' Transaction ' of last October. 
Mr. Mayall's abilities as a pbotograpber cannot be questioned; 
therefore, when the Fellows present at the reading of his paper heard 
the detailed analysis of the photo-micrographs, they must have felt 
that beyond this there was no appeal ; not so with his incidental 
remarks on the comparative qualities of various objectives : and, 
indeed, the accuracy of these remarks was immediately challenged. 
It is, then, with regret and disappointment that I now see the 
valuable, because authoritative, portions of the paper suppressed, while 
the secondary or incidental parts of the original memoir are amplified, 
and the contained opinions somewhat rashly enforced. 
On the comparative merits of high powers — wet and dry — and the 
absolute superiority of either, there are not probably in England a 
dozen microscopists thoroughly qualified to decide. The arbiter must 
have had lengthened experience with all kinds of objects, and every 
variety of illumination ; but as Mr. Mayall, jun., can scarcely have 
had the former, and, regarding methods of illumination, seems to 
content himself with one — the oblique, I should beg your readers 
to suspend judgment in his suit of Immersion versus Dry Objectives 
until competent authority gives a decisive verdict. Perhaps the 
Council of the Royal Microscopical Society may be induced to 
appoint a sub-committee to inquire into this important matter. 
To Mr. Mayall should be given every credit for good intentions. 
His grief can be imagined when forced by a bitter sense of duty to 
denoimce — mildly and with all scientific propriety, but still to 
denounce — our microscopes and all who use them. But let him take 
heart; our English opticians are again taking up this old novelty — 
the immersion system ; and if found really serviceable, no doubt it 
will be adopted. In the meantime, and at the worst, our glasses 
may pass as very respectable mediocrities. They resolve the finest 
tests, and are actually preferred by the American photographers 
for the most exquisite micrographs ever taken, of the finest lines 
ever seen. 
Without having more than an average experience and skill with 
the microscope, even I — a mere " amateur with a wonderful Jth — 
can readily discover facts in direct contradiction to Mr. Mayall's 
observations. Unlike that gentleman, I meet no difficulty whatever 
in finding evidence that the resolution of lined objects is almost 
entirely a question of large angle in the objective ; that comparatively 
low powers (such as 4^ths and -^ths), with apertures above 130°, show 
the fine longitudinal markings on S. gemma, and that higher powers 
of similar angles fully verify the results. The statement that im- 
mersion-lenses are in effect reduced to a certain small angle, beyond 
which a law of refraction forbids them to work, seems entirely nega- 
tived by the fact that one of these objectives bore in my presence the 
very greatest possible obliquity in the light, without giving the slightest 
indication of black-ground illumination, — an effect easily produced with 
any glass of angle less than 140°. 
