THE HICBOSCOPE. 
471 
are useful lessons to tlie student. But for most errors of inter- 
pretation, the simplest remedy is the use of low powers until 
sufficient experience is gained to allow of higher powers being 
usefully employed. 
In handling the eye-pieces and object-glasses, care should be 
taken to touch the glass surfaces themselves as little as possible, 
as they readily become dimmed by contact with the hands, or 
even by the moisture exhaled on too close an approach. A 
piece of wash-leather should be always at hand, as it is the best 
material for cleansing the glasses either from dust or moisture ; 
and if any water is used, as in examining’ animals or vegetables 
in fluid, great caution should be exercised in keeping the object- 
glass dry ; or if by accident it gets wetted, it should be wiped 
as soon as possible. This caution is particularly necessary when 
salt-water is used, and the microscope should be carefully 
cleansed of the least particle of it before being put away, other- 
wise unsightly corrosions, verdigris, and impaired action of the 
mechanical parts, will soon result. Indeed, every one who values 
his microscope will take the greatest care that it does not suffer 
from thoughtlessness, or inattention to such simple precautions. 
In the foregoing sketch I have only alluded to such apparatus 
as may be regarded as essential to working with the microscope,, 
but there are still many additional pieces which the student 
may with advantage add from time to time, as his experience or 
his wants increase. Of such accessory apparatus several are 
contrivances for improving the illumination, of which some are 
luxuries, and others are really useful, and even essential to the 
proper examination of special and peculiar objects by the ex- 
perienced and professed microscopist. The LieberJciihn speculum , 
for examining opaque objects, and Wenham’s Parabolic Reflector, 
for obtaining perfect definition under high powers, are examples 
of these. The polarizing apparatus I have altogether omitted, 
because any satisfactory description and explanation of it would 
have increased this paper beyond desirable limits ; it can only 
be here stated that the polariscope is a useful addition to 
a microscope, particularly if it be chiefly used as a recreation, 
the beautiful chromatic effects which are produced by it being 
in the highest degree curious and fascinating’ ; and even the 
scientific microscopist will sometimes find it of real service. 
Micrometers, glass slides with fine and regular hues for the 
measurement of minute objects — and finders, by means of 
which any special object of the minutest size may be at once 
placed under the object-glass, without the trouble of half an 
hour’s search, are also useful additions. Other accessories relate 
to the examination of living objects. Usually, the prepared object 
is placed upon a flat glass ; but if it is a minute living animal, it 
may be placed either on a thicker glass, hollowed out in the middle 
2x2 
