above the furface o f the glafs. When it is fo difpofed, hold it as
level as you can over the clear part o f a fire that is not too fierce,
or over the flame o f a candle, at a diftance proportionable Jo the
degree of heat it requires, (which experience only can direft) and
watch it very carefully till you difcover the faline particles
beginning to gather and looE'white, or of fome other colour, .at
the extremities of the edges; then having adjufted the microfcope
before-hand for it’s reception, armed with the fourth glafs, which
is the fitteft for moll of thefe experiments, place it under your
eye, and bring it exaftly to the focus o f the magnifier; and,after
funning over the whole drop, fix your attention on that fide
where you obferve any increafe or pufhing forwards of cryftalline
matter from the circumference towards the center.
This motion is extremely flow at the beginning, unlefs the drop
has been over-heated, but quickens as the water evaporates, and
in many kinds, towards the conclufion, produces configurations
with a fwiftnefs inconceivable, compofed o f an infinity of parts,
which are adjufted to each other with an elegance, regularity,
and order, beyond what the exafteft pencil in the world, guided
by the ruler and compafs, can ever equal, or the moft luxuriant
imagination fancy.
When aftion once begins, the eye cannot be taken off, even
for a moment, without lofing fomething worth obfervation; for
the figures alter every inftant, till the whole procefs is over; and
in many forts, after all feems at an end, new forms arife, different
entirely from any that appeared before, and which probably are
owing to fome fmall quantity of fait o f another kind, which the
other feparates from, and leaves to aft, after itfelf has done; and
in
in fome fubjefts three or four different forts are ebfervable, few
or none being fimple and homogeneous.
When the configurations are fully formed, and all the water
evaporated, moft kinds of them are foon deftroyed again by the
moifture or aftion of the air upon them; their points and angles
lofe their fharpnefs, become uneven and defaced, and moulder as
it were away; but fome few are permanent, and by being in-
clofed between glafl'es, they may be preferved months or even
years.
It happens oftentimes that a drop o f a faline folution can
hardly be fpread on the flip o f glafs, by reafon of the glafss
fmoothnefs, but breaks into little globules, as it would do were
the furface greafy: the way to prevent this is', by rubbing the
broken drop with your finger over the glafs, fo as to leave die
glafs fmeared with i t ; on which ftneared place, when dry, another
drop o f the folution may be fpread very eafily in what form
one pleafes.
It fometimes happens, that when-a heated drop is placed
properly for examination, the obferver finds he can diftinguifh
nothing; which is owing to faline fleams that rife from the drop
cover, and obfcure the objeft glafs, and therefore muft immediately
be wiped away with a foft cloth or leather.
In all examinations by the microfcope of faline folutions, even
though made in the day-time, you muft ul'e a candle; for the
configurations being exceedingly tranfparent, are rendered much
more diftinguilhable by the brown light a candle affords, than by
• * the