346 
fatigue of long-continued observation is greatly 
diminished. Such minutia may appear too 
trivial to deserve mention; but no practised 
microscopist will be slow to acknowledge their 
value. At the inclination we have mentioned, 
the de of the stage from the horizontal 
position will not be such as to render it neces- 
sary to confine the objects with more than a 
slight force, and accordingly they may be 
moved by the hands with considerable free- 
dom ; and light objects may be placed upon a 
slip of glass without any confinement, or co- 
vered with talc if necessary, and yet be in 
little danger of falling off it. These are con- 
yeniences which are of more value in practice 
than they may appear in theory; for it will 
often be found that the saving of a little time 
in the adjustment of the microscope is of 
great importance in the observation of objects 
which are undergoing change. There are some 
objects, however, which can only be seen in a 
vertical microscope, as they require to be viewed 
in a position nearly or entirely horizontal ; such 
are dissections in water, saline solutions under- 
gving chrystallisation, &c. For other purposes, 
again, the microscope should be placed hori- 
zontally, as when the camera lucida is used 
for drawing or measuring. It ought, therefore, 
to be made capable of every such variety of 
ition. 
4. The last principle on which we shall 
here dwell is simplicity in the construction and 
adjustment of every part. Many ingenious 
mechanical devices have been invented and 
executed, for the purpose of overcoming dif- 
ficulties which we cannot but regard as trivial. 
If all these were combined in one instrument, 
a degree of complexity would be thereby 
engendered, which would prevent it from be- 
ing generally available. Our own experience 
leads us to the conclusion, that a moderate 
amount of dexterity in the use of the hands is 
sufficient to render most of these superfluous ; 
and without such dexterity, no one, even with 
the most complete mechanical facilities, will 
ever become a good microscopist. We shall 
hereafter describe, however, some of those 
which are in most general use ; premising that 
we cannot speak from much experience of 
their applicability, since we have ourselves 
found no difficulty in doing without them, as 
we recommend our readers to do. Although a 
large box, well filled with glittering brass im- 
Pravnonts of various shapes and sizes, may 
have a very inviting appearance, it will often 
be found that these are more for show than use, 
and add to the expense of the instrument in a 
proportion far exceeding their utility. Among 
the conveniences of simplicity, the practised 
peaevennptat will not fail to recognize the 
saving of time effected by being able quickly 
to set up and put away his instrument. Where 
a number of parts are to be screwed together 
before it can be brought into use, interesting 
objects as well as time are not unfrequently 
lost; and the same cause will often occasion 
the instrument to be left exposed to the air and 
dust, to its great detriment, because time is 
MICROSCOPE. 
required to put it away. With those who are 
not practised in mocha a i oe h 
is especially necessary ; in we have often 
Seen) a slight advantage on the side of sim- 
plicity of arrangement cause an inferior in- — 
strument to be preferred to a superior one, 
Yet there is, of course, a limit to this simpli- 
fication; and it ought never to interfere with 
due attention to the principles already spe-— 
cified. ty 
Before proceeding to notice any of the ordi- 
nary forms of stands for simple or 
microscopes, we shall make a few remarks on 
the best means of carrying on a dissection — 
under a magnifying power. The simplest of 
all means of effecting this, where the objectis 
large and opaque, and a low magnifying power 
only is requisite, is to fasten it down upona 
board, to any part of the edge of which may 
be afhxed, by means of a small clamp, a 
jointed stem, carrying a socket or cell, into 
which a lens mounted in the usual 
may be dropped. This stem, being 
of movement in every possible direction, but 
having also sufficient stiffness in its joints 
remain in any position in which it 
placed, appears to us preferable to any other 
pes of supporting the lens. The object 
e illuminated, if necessary, by light condensed 
through a convex lens, or reflected from a con-— 
cave mirror. Pe se tenant must pay 
on under fluid, the only variation necessary 
the use of a shallow trough, instead of a board, 
which may be filled with water, dilute spirit, 
or oil of turpentine, as the case requires; to — 
the edge of this trough the clamp me be fixed 
in the most convenient position ; the bot- 
tom of it (if of metal) may be covered with a 
piece of cork, or a layer of resin and 
wax, for the purpose of receiving the pins 
necessary to fix the object. Where the object 
is smaller, and the dissection may be carri 
on under a higher magnifying power, we 
strongly idee the use of -Mr. Slack's 
dissecting microscope, of which a description 
and figures may be found in the 49th volume 
of the Transactions of the Society of Arts.* 
Dissecting instruments.—The instruments 
employed in microscopic dissection must of — 
course vary with the nature and size of the 
object. The following will, we think, be found _ 
most generally useful. Small pointed scalpels. 
The iris-knife is a convenient size and form 
for many purposes. Scarpa’s curved catarac 
needle is an instrument which we have found 
extremely serviceable. Fine scissors, one leg 
of which should be fixed in a long handl 
and the other kept apart from it by a spriz 
so as to close by the pressure of the finger and 
to open of itself; the blades should both be — 
pointed and sharpened on a hone; these will 
* [Mr. Powell, the optician, Clarendon-strect, — 
Somers’ Town, has enlarged and improved con- 
siderably Slack’s dissecting microscope; and Mr. 
Ross, of Regent-street, has also on sale a conve- 
nient form of dissecting microscope, which is deli- 
neated in the Penny Cyclopedia, art. * Micio- 
scope.’—Ep.] oy 
i 
pais 
