238 Transactions of the Boyal Microscopical Society. 
The new Jth by Powell and Lealand must, if fairly considered, 
be regarded as a convincing proof that a comparatively low power 
can be made to do work for wbicb the highest that can be con- 
structed have been supposed necessary. It likewise indicates the 
narrow limits within which a fine large-angled glass, working near 
the object, can be made to operate with advantage. If this remark- 
able objective is compared with an ordinary -Jth, no admiration of 
its merits will prevent complaint of its limited amount of penetra- 
tion ; but it is in fact an improved substitute for a far higher power, 
and in that respect deserves high praise. Few, if any, of the finest 
powers previously made would give a clear view with anything like 
the magnification which deep eye-pieces afford with this objective. 
By the kindness of Mr. Lettsom, who was one of the first to order 
and obtain one of these glasses, the writer has been able to experi- 
ment with it. The E eye-piece of Boss's series, giving a magnifica- 
tion of about 2000 linear, suits it as well as the lowest eye-piece 
suits ordinarily fine glasses ; and the view that can be thus obtained 
of such an object as P. angulatum surpasses in beauty and bril- 
liancy anything seen before. With appropriate illumination there 
is a marvellous stereoscopic rotundity of the beads, the interspaces 
are remarkably large, and the shadows are wonderfully sharp. It 
would obviously bear a much deeper eye-piece than E, and was 
exhibited to this Society with one stated by Messrs. Powell and 
Lealand to bring it up to 4000 x . 
Under special conditions this objective may serve the naturalist 
and physiologist in a remarkable manner. It has enough penetra- 
tion to show the internal structure of small rotifers, and it, together 
with previous high powers by the same optical artists, proves that 
Professor Abbe is quite wrong in his dictum that no microscope can 
show anything beyond that which a sharp eye can detect with 
800 X . To say nothing of lined objects, Messrs. Dallinger and 
Drysdale have been indebted to the much higher magnification 
obtained by gV^hs for some of the most valuable information con- 
cerning minute germs they have laid before us. 
It may be impossible to obtain such enormous magnification 
and resolving power as this glass will give without an angle of 
aperture and an approximation to the object which is incompatible 
with much penetration, and in using it we must compare it with 
sVths and sVths rather than with an ordinary ith. So compared, its 
working distance will be pronounced large, and its penetration con- 
siderable for the power. There is with it, however, a rapid, almost 
violent, transition from perfect performance when all its conditions 
are complied with, to bad performance, and no performance, if the 
object is not sufficiently flat, placed exactly in the best position, 
and illuminated in the best way. 
It would be well worth trying whether the same principle of 
