NOTES AND MEMORANDA. 
173 
with a quarter. The drop of water gives an immersion lens a larger 
angle of aperture and more light, besides other advantages, and it has 
therefore, other things being equal, greater resolving power. The 
Doctor says that his skill, or unskilfulness, as a microscopist, were all 
constant factors, so that the superior performance seemed certainly 
due to the superior qualities of the higher power lens. Now, certainly, 
no greater fallacy could be than such an hypothesis. In unskilfulness 
chance is constantly occurring to deceive, and cannot be provided 
against. We think we can almost say, without exaggeration, that in 
the majority of instances an unskilful microscopist will select the 
poorer of two objectives as the one he can do the most with. And this 
is not very strange when we come to consider ; for the finer a lens is, 
the more perfect must be the conditions for it to perform well, and 
the greater is the skill required in its management. A tyro, who is 
filled with admiration with the conduct of a French commercial 
objective that a microscopist would regard of no value whatever, 
would probably not be able to see anything with a fine Powell and 
Lealand ^th, so perfect must be all the conditions in order for it to 
disclose its exquisite powers. Dr. E., in comparing the resolving 
powers of the two ^V^hs, found that the transverse strife of Surirella 
gemma were easily shown, but that the finer longitudinal stride were 
not distinctly visible by gaslight. On our part, we never find any 
difficulty in bringing into view the transverse strice, with any ordinarily 
good quarter or even half inch, and we have no trouble in showing, 
by lamplight, the longitudinal lines with our Powell and Zealand's 
-jig^th, Verick's No. 10, Gundlach's German No. 7, Seibert and Krafft's 
^th, &c., &c. ' Under the employment of monochromatic sunlight,' 
the Doctor goes on to say, ' these faint markings, which Frey says are 
" only to be mastered with much pains," are clearly visible, even 
under Wales' qV*-^-' Now, we are not the owner of a Wales' ^^th, but 
we are of an eighth by him, and from its performance we do not think 
that with a little skill in its management there would be any difficulty 
in the ^^^th mastering the longitudinal striae without the aid of mono- 
chromatic sunlight Not only does Seibert and Krafft's ^^^th bring out 
these faint lines without the aid of the blue cell, but even their |^th 
does it with proper amplification- In testing with the Podura scales, 
the result of his comparative trials with central light was that the 
definition of the note-of-exclamation-marks afforded by the ToUes' 
Jg^th immersion was somewhat superior to that given by the Wales' 
immersion ^V^h, and the Powell and Lealand's dry -^Qth, although the 
advantage over the latter was very slight. We do not think that the 
Doctor's judgment in this matter would have much weight with micro- 
scopists. The failure to define the longitudinal lines of the Surirella 
gemma with the glasses of such eminent makers as ToUes, and Powell 
and Lealand, implies such a want of skill in manipulating very fine 
lenses of high power, as to render an opinion valueless in regard to 
any comparative merit. In the use of the microscope in the study of 
pathology, Dr. Richardson has undoubtedly done a great deal of work, 
and, in that department, has used the instrument to advantage, as the 
results of his labours have shown ; but, to judge from his paper, as a 
o 2 
