METHOD OF USING THE MICROSCOPE. 
327 
2cl. On the management of the light depends in a great measure 
the distinctness of the vision: and as, in order to have this in the 
greatest perfection, we must adapt the quantity of light to the nature 
of the object, and the focus of the magnifier, it is therefore necessary 
to view it in various degrees of light. In some objects it is difficult to 
distinguish between a prominence and a depression, a shadow or a 
dark marking; or between a reflection oi light, and whiteness, which 
is particularly observable in the eyes of LibelMa and other insects ; 
all of them appearing very different in one position from what they do 
in another. The brightness of an object likewise depends on the 
quantity of the light, the distinctness of vision, and on legulating the 
quantity to the object; for some will be .in a manner lost in a quan- 
tity of light scarcely sufficient to render another visible. 
The Ibdit of a lamp or candle is generally better for viewing mi- 
croscopic" objects than daylight, it being easier to modify the former 
than the latter, and to throw it upon the objects with different degrees 
of density. The best lamp that can he used for this purpose is the 
one invented by Count Humford, which moves on a rod, so that it 
may be easily raised or depressed. The light of a candle or lamp 
is increased, and more directly thrown upon the reflecting mirror 01 
object, by means of a convex lens mounted on a semicircle and stand, 
so' that its position may be easily varied. If the light thus collected^ 
from a lamp be too powerful, it may be lessened by placing a piece ot 
thin writing-paper, or a piece of fine grayed glass, between the object 
and the reflecting mirror. Thus a proper degree of light may be ob- 
tained, and diffused equally all over the surface of an object a cir- 
cumstance which ought to be particularly attended to; for it the light 
be thrown irregularly upon it, no distinct view can be obtained. 
The examination of objects so as to discover truth, requires a great 
deal of attention, care, and patience ; with some skill and dexterity, to 
he acquired chiefly by practice, in the preparing, managing, and apply- 
ing them to the microscope. 
Whatever object offers itself as the subject of our examination, the 
size, contexture, and nature of it arc first to be considered, in order to 
apply it to such glasses, and in such a manner, as may show it best. 
The first step should always be to view the whole together with such 
a magnifier as can take it in all at once ; and after this the several 
parts of it may the more fitly be examined, whether remaining on the 
object, or separated from it. The smaller the parts are which are to 
he examined, the more powerful should he ihe magnifiers employed. 
The transparency or opacity of the object must also be considered, anil 
the glasses employed accordingly suited to it; for a transparent object 
will bear a much greater magnifier than one which is opaque, since 
the nearness that a glass must be placed at, unavoidably darkens an 
