466 
POPULAR SCIENCE REVIEW. 
moveable in all directions, throws up the light which it reflects 
from a window, or a lamp, upon the transparent object which 
it thus illuminates from beneath. The upper part of this 
column is provided with a pair of large millecl-heads, by 
turning which, the tube of the microscope, together with the 
solid cross-piece to which it is fixed, can be raised or lowered 
by means of a rack-work attached to a short stem which slides 
up and down in the upper part of the column. By this means 
the focus can be adjusted without the necessity of moving the 
stage, which in all the best microscopes is a fixture to the 
lower column. This is termed the coarse adjustment, and, for 
Ioav magnifying powers, is all that is needed for regulating the 
focus. 
The tube of the microscope itself, which is thus raised 
and depressed, has the objective , or object glass, at its 
lower extremity, and this can be unscrewed (fig. 3) and 
replaced by another power at pleasure ; and at its upper 
extremity is the eye-piece, which is also readily pulled out 
(as at fig. 1), either for the purpose of cleansing it, or for the 
insertion of another kind of eye-piece. About midway up the 
tube is a small milled-head (seen edgewise) connected with 
what is termed the fine adjustment. A very slight movement 
of this milled-head alters the focus, when high powers are 
used, so that, having brought the object roughly into focus by 
means of the coarse adjustment, the utmost 
precision and the clearest definition may 
readily be obtained by a turn or two of the 
fine adjustment. Finally, in the description 
of this microscope only one thing more need 
be noticed, and that is, that the whole in- 
strument is suspended (neither too stiffly nor 
too loosely) upon the two screws at the upper 
part of the pillars of the stand, so that it may 
be placed in a vertical, an inclined, or even 
a horizontal position, at pleasure, without 
moving the stand. This is an important 
advantage ; for whilst various degrees of obli- 
quity are often requisite to meet the convenience of the observer 
as he sits in his chair, or to take advantage of the position of 
the light, it is sometimes desirable to place the instrument in 
a vertical position, as when examining objects in water, while 
the horizontal is a no less useful position for certain purposes. 
Let us now suppose the microscope placed upon a firm table, 
and the observer, with all his apparatus ready at hand, seated 
before a Avindow. This leads us to make some remarks upon 
the illmnination of the object. Daylight, when it can be used, 
is preferable to artificial light, — not direct sunlight, Avhich is 
Fig. 3 . 
