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brafs tube, which contains the lenfes for condenfing the light, and
throwing it upon the objeft; there is a fecond tube within that,
marked 9 and 10, which may be placed at different diftances
from the objeft by the pin 11.
T When this ftage is ufed as a Angle microfcope, without any
reference to the lucernal, the magnifiers, or objeft lenfes, are to
be fcrewed into the hole 12, and to be adjufted to a proper focus
by the nut 13.
N. B. A t the end A B o f the wooden body, there is a Aider,
which is reprefented as partly drawn out at A ; when quite taken
out, three grooves will be perceived, one o f which contains a
board that forms the end of the box, the next contains a frame
with a greyed glafs, the third, or that fartheft from the end A B,
two large convex lenles.
O f th e L am p .
Fig. 3, reprefents one of A rgand’s lamps, which are the moll
fuitable for microfcopic purpofes, on account o f the cleamefs,
the intenfity, and the fleadinefs of the light. The following account
of the method of managing them, with other obfervations,
is copied from an account given by Mr. Parker with thofe he fells.
The principle on which the lamp afts, confifts in difpofing
the wick in thin parts, fo that the air may come into contafl with
all the burning fuel, by which means, together with an increafe
of the current o f air occafioned by rarefaftion in the glafs tube,
the whole o f the fuel is converted into flame.
6
The wicks are circular, and, the more readily to regulate the
quantity of light, are fixed on a- brafs collar with a wire handle,
by means o f which they are raifed or deprefled at pleafure.
T o fix the wick on, a wood mandril is contrived, which is
tapered at one end, and has a groove turned at the other.
The wick has a felvage at one end, which is to be put foremoft
on the mandril, and moved up to the groove; then putting the
groove into the collar o f the wick-holder, the wick is eafily
pufhed forward upon it.
The wick-holder and wick being put quite down in their place,
the fpare part o f the wick fhould, while dry, be fet alight, and
fuffered to bum to the edge o f the tubes ; this will leave it more
even than by cutting, and, being black by burning, will be much
eafier lighted; for this reafon, the black fiiould never be quite cut
off.
The lamp fhould be filled an hour or two before it is wanted,
that the cotton may imbibe the oil and draw the better.
The lamps which have a refervoir and valve, need no other
direftion for filling than to do it with a proper trimming pot,
carefully obferving when they are full; then pulling up the valve
by the point, the refervoir, being turned with the other hand,
may be replaced without fpilling a drop.
Thofe lamps which fill in the front like a bird-fountain, muff
be reclined on the back to fill, and this fhould be done gently,
that