MICROSCOPE. 
and its portability is a great recommendation. 
The one in our own possession is packed, with 
its tripod, into a box whose outside dimensions 
are 7% inches by 5, and its depth only 2, and 
this also contains a short body with meniscus 
eye-piece, four ordinary magnifiers, and three 
doublets and triplets, which may be used 
singly or as objectives, illuminating lenses and 
Speculum, aquatic boxes, and other small ap- 
paratus,—the weight of the whole being no 
more than 2% lbs, although a magnifying power 
of 450 diameters, with sufficient penetration to 
exhibit the markings on the Podura, and with 
perfect steadiness, may easily be obtained by it. 
The instruments we shall now describe are 
not adapted for use in any other way than as 
compound microscopes. Their size and weight 
are such as would render them far less conve- 
nient than the smaller forms already described 
for use with simple lenses, although there is no 
other reason why they should not be thus em- 
sya Every constructor of microscopes has 
is own favourite model ; and there are few re- 
cently made instruments of the highest class 
which do not possess some particular recom- 
mendations. Amidst the numerous claimants 
to our notice, we shall select two; of which 
the first is the form adopted by one of the best 
constructors of achromatic objectives in this 
country ; and the second is the one which we 
have ourselves had in use for several years, 
and which we do not desire to lay aside for 
any we have seen. With respect to the former, 
our limited space compels us to refer to the 
article Microscope in the Penny Cyclopedia, 
where a delineation and full description of Mr. 
Ross’s Microscope will be found.* 
We shall now describe the microscope 
* [Without wishing in the least degree to detract 
from the merit of Mr. Ross’s microscope, (to 
which, on the contrary, he bears willing testi- 
mony,) the Editor deems it but justice to refer 
to a very beautiful instrument constructed by Mr. 
Powell, which he has employed for some time, and 
which is also used by several observers in this city. 
The body of the microscope moves on a triangular 
bar, having a bearing of three inches, which ren- 
ders it very steady. The coarse adjustment is ob- 
tained by a rack and pinion, attached to which are 
two large milled heads, which allow of the body 
being adjusted with either hand. The fine adjust- 
ment has also two milled heads, only two inches 
apart from the coarse one, and their axis being 
horizontal and parallel to each other, renders the 
motion of the hand from one to the other perfectly 
easy, withont removing the eye from the body of 
the microscope. The stage is seven inches square. 
e convenience of its being thus large is, that the 
hands do not interfere with the object when adjust- 
ing it. The heads that move the stage have their 
axis in the same line, and so placed that with the 
same hand the stage may be moved in all direc- 
tions ; this is convenient when viewing an object, 
the surface of which is very irregular; with the 
right hand you can move the stage, and there being 
two heads to the adjustments for the body, with 
the left the object can be adjusted into focus. There 
are likewise two milled heads to one motion of the 
stage, by which means both hands may be employed 
at the same time, which is sometimes requisite. 
On the same bar that the body rests, moves the 
‘* achromatic condenser,” by which arrangement it 
4s certain to move in the same line with the body, 
349 
which we have ourselves been accustomed to 
employ, and state what we regard as its advan- 
tages; not omitting to notice the objections 
which may be brought against it, and bearing 
in mind that every microscopist is naturally 
most partial to the form which he has himself 
adapted to his own ideas of convenience. It 
is principally constructed according to the 
plans of Mr. Pritchard and Dr. Goring ; and 
we may observe in limine, that the objections 
which have been brought against any form of 
construction in which the body is screwed by 
its lower extremity to a horizontal arm, as 
placing it in the most unfavourable position for 
vibration, independently of the stage, are ap- 
plicable only to instruments which are not 
made with sufficient solidity; for, having had 
an opportunity of comparing the quality in this 
respect, of Mr. Ross’s microscope, with our 
own, the two being placed in exactly the same 
circumstances, we could not find that there 
was any inferiority on the part of the latter. 
It must be borne in mind, that every increase 
in the size and power of a microscope must be 
accompanied by more than a corresponding 
increase in solidity, in order to guard effec- 
tually against oscillation. 
The stand or basement is a slab of solid 
mahogany 12 inches square and 14 inch thick, 
loaded with lead at the corners, aud having a 
strip of thick baize, about 1$ inch broad, glued 
round the edge of the under side; the whole 
weight bears upon the baize, which does not 
readily communicate vibrations; and the large 
surface over which the pressure is distributed 
gives the instrument a degree of imperturba- 
bility which would scarcely have been antici- 
pated. The slab is surrounded by a slightly 
elevated rim ; and it thus serves as a most con- 
venient little table, on which the various pieces 
of apparatus required for microscopical obser- 
vation may be carried about with the instru- 
ment without any danger. The pillar of the 
microscope carries at its lower extremity a 
screw, above which is a fange or shoulder of 
2 inches diameter; the screw is received into 
a socket let into the wooden foot, and firmly 
attached to it, and itself having a shoulder of 
equal size; so that, when the pillar is firmly 
screwed down upon it, there is not the least 
tendency to vibration between the two. The 
socket is not let into the middle of the base, 
however; but its centre is only 24 inches from 
one of the sides, and 9%, therefore, from the 
other; so that, in fact, when the microscope is 
placed vertically, the centre of the stage pretty 
nearly corresponds with the centre of the foot. 
The object of this is to give a decided prepon- 
derance in weight to the front of the foot in all 
positions of the microscope ; for we are inclined 
to think that much of the oscillation so fre- 
quently complained of in microscopes is to be 
which is most essential, for unless it did 80 when 
using different power object-glasses, the axis of the 
lenses would not coincide. There are many other 
conveniences and improvements to this microscope 
which cannot be mentioned in this, brief notice.— 
ED.], 
