THE MICROSCOPE. 
467 
too powerful^ but strong; diffused liglit; wliicli can be used 
with much more comfort than artificial fight; and at the same 
time affords a more satisfactory view of the object under 
examination. But as it generally happens that the microscope 
is taken out when the busy labours of the day are over; some 
kind of artificial fight is requisite ; the great desideratum being 
a fight which will not flicker; but will burn steadily; and give 
as pure a flame as possible. Gas may easily be brought down 
from the burner by an elastic tube communicating with a 
portable lamp upon the table ; and; for those who have gas, 
this is; perhaps, the simplest expedient. The expensive solar and 
argand burners are, however, now in a great measure superseded 
by very inexpensive and manageable paraffin lamps. A lamp 
of this kind can be purchased at an oilman’s or lamp-seller’s 
for prices varying from one shilling upwards ; a really elegant 
lamp, particularly when lighted, being obtainable for the small 
sum of two shillings, or half a crown. The oil burned in these 
lamps requires, however, a word of comment and caution. The 
ordinary cheap paraffin oil is liable to give off an explosive 
vapour, which might lead to serious accidents. A simple 
test of the quality of the oil is to pour a little of it upon a 
plate or saucer, and apply a fight to it. If it take fire, it is 
dangerous ; but if it does not burn, it may be freely used. By 
purchasing the oil termed Belmontine, however, all danger is 
avoided, and a pure fight is obtained at a very small cost, it 
being only one shilling and twopence per quart. A lamp of 
this kind may be placed as near the reflecting mirror as necessary, 
and maybe raised or depressed by blocks at pleasure ; while 
the glare upon the eye from the lamp itself may be easily 
avoided by suspending a shade of cardboard, or other similar 
material, in front of the eye-piece of the microscope. By 
turning the mirror about, the fight is easily directed upwards 
through the transparent object, and regulated, either by slight 
eversion of the mirror, or by the use of a smaller stop in the 
diaphragm. If, however, it be desired (as is often the case) to 
examine an object which is impermeable to the fight thus 
thrown up by the mirror, another method of illumination 
becomes necessary. For this purpose the condenser (fig. 4) is 
employed. It usually consists of a, large plano-convex lens, 
and is sometimes mounted upon the microscope itself, being 
readily turned aside when not used, or towards the object, 
when required, by means of a joint or elbow. In the larger 
microscopes, however, this condenser, or bull’s-eye, is mounted 
upon a stand (as in the figure), upon which it slides up 
and down, the glass being fixed upon a stem which is 
received in a tube, thus allowing of its being freely turned in 
a vertical direction; while the tube itself admits of a horizontal 
