
286 THE NORTHERN MICROSCOPIST. 
trayed where least expected. If we admit that the highest aperture can be 
utilized in a 1-16th objective, it becomes amusing to hear anyone speaking of 
a high angle 1-35th inch or 1-5oth inch. I said at the commencement, that it 
was my contention that there should always be maintained something like a 
just apportionment of aperture and amplification. If you wish to see an object 
as a whole, given a suitable power, that aperture will suffice which will give you 
the best image (mind you) as a whole. This proposition embraces the whole 
uestion. if you wish to see only a portion of the same object, that portion, 
for the time being, constitutes the whole of what you look at. Here, again, you 
will choose a power and aperture sufficient to produce the best a of the 
part as a whole, You will scarcely believe me, but at this point I nearly broke 
down; I could not, for the life of me, recollect what merits in particular were as- 
cribed to powers of wide aperture. Of course I knew their use had been strongly 
advocated for some considerable time, or I should have come to the conclusion 
they were recommended merely to make a use for the new aperture shutter. I 
have always been under the impression that a working microscopist required a 
range of powers. Possessing these powers, I never could see the advantage of 
excess of aperture in any given objective, when by the use of a higher-powered 
objective a better result could be obtained. Latterly, however, it has been 
assumed (so I take it) that, two or three lenses only are required for practical 
work, providing, of course, they are lenses of wide aperture. This, I venture 
to assert, is a most pernicious doctrine. This contention rests upon a variety 
of assumptions incompatible with each other. We are told that “ the use of 
deep eye-pieces and the aperture shutter any required amplification or amount 
of penetration is at our disposal. To this I would say, “‘ Yea, verily! of a sort.” 
I must here propound some propositions, and I shall be glad to let copies be 
taken for consideration. Given a certain power and a certain aperture, say an 
inch of 35°. If this aperture is necessary to constitute a good lens, why is it 
not impaired when cut down to an aperture of 16°? If the i given by the 
aperture of 16° is not inferior, why have an aperture of 35°? Or, again, with 
the same objective, increase the amplifying power, by a deep eye-piece, to 160 
diameters : is, or is not, the result obtained inferior to that given by 
diameters? If not, we must conclude that an aperture of 35° is sufficient m 
relation to power for an amplification of 160 diameters. If the result is inferior, 
wherein lies the merit of deep eye-piecing ? 
Whatever authority you turn to, you are always warned against accepting 
results obtained by this means. Increased power thus got is not, be it remem- 
bered, increased magnification of the object itself; it is merely an enlargement 
of the size of the image formed in the first instance by the object glass, Abbé 
says (and I may here remark, if he is thrown overboard by his old friends, he 
will find plenty of new), and the same opinion is held by Carpenter, Beale, 
Marsh, T. Davies, and others,—‘‘ That forcing a high amplification, by this 
means, from a low-power objective is always connected with considerable loss 
of ness of the image, owing to the magnification of the resid aberra- 
tions which are inherent even in the most finished constructions,” It is also 
certain that Dallinger, as I shall presently show, and who may be taken as 
a leading authority in connection with everything relative to the use of high 
powers—does not make use of deep eye-pieces except as a last resort. Two 
serious objections to the use of object glasses of wide aperture are, loss of work- 
ing distance between the object and the objective, and want of penetration or 
focal depth by which involved structural relation can be easily made out. The 
importance of these two requirements in low and medium powers are indis- 
pensable, and in this assertion I shall, I think, be borne out by every member 
who works with ey Raper eu ong A accomplishment in a lens will 
ever compensate for these useful attributes. . Carpenter, king of pene- 
tration or focal depth, says, “The possession of a high Feit olny F ito 
essential to the satisfactory performance of those objectives which are to be 
