The Durham daily globe., 1892-10-08
THE VALUE OF DUST.
Its Particles Form Free Surfaces for the
Collection of Vapor

Its Particles Form Free Surfaces for the
Collection of vapor.
How can invisible particles be brought
within the range of our vision: That
was one Of the first of the many marvel
Gus discoveries Of Mr.. John Aiken, F.
X. b, Falkirk. distinguished physicist.
whose remarkable work has revolution
lZed a branch of meteorology. He
showed that without dust in the air
there could be no fogs, no mist, no cloud
and probably no rain. The particles of
dust are the free surfaces, which, under
certain conditions, attract the water
vapor Of the atmosphere to form fog.
Invisible before, they become visible
when clothed all over with the moisture;
unseen as dust, they become distinct as
fog particles.
This can be easily verified. If ordi-
nary air be forced through a filter Of
cotton wool into a glass receiver, it is
deprived OF all its dust particles. Let
steam be introduced into this receiver
from boiler, no change will be OBJ
served; the vessel is quite transparent.
Bat If jet of steam be introduced into
similar vessel containing ordinary air,
1t viii be seen rising in a dense cloud;
then u beautiful fog will be formed, so
dense that it cannot be seen through. In
the former case, when there was no
dust in suspension, the air remained
clear; in the latter case, when the ordi-
nary atmospheric dust was in the YES
sci, fog at once appeared. The invisible
dust then is detected by the introduc-
tion of water vapOr.
Until very lately it was thought that
particles Of water vapOr combined with
each other to form a cloud particle, but
it is now found that some solid body,
however small, is required for this
formation. In fact, when there are no
dust particles on which the water vapor
at n proper temperature and pressure
can cOndense, there is at present no
knowledge as to the point at which the
change will take place. But the fine
particles Of dust in the air act as free
surfaces on which the water vapor con-
denses into fog. When there is abund
anCe of dust in the air and little water
vapOr present there is an Overpropor-
ton Of dust particles, and the fog par
ticles are III consequence closely packed,
but light IN form and small in size, and
take the lighter appearance Of fog. Ac-
cordingly, if the dust is increased in the
air, there is proportiOnate increase of
fog.
But on the other hand if the dust
particles are fewer i'll proportion to the
number of molecules Of water vapor,
each particle soon gets weighted, springs
into visible existence as if by a creative
hand, and falls in mist or rain. If the
water vapor had no dust at all on which
to settle, it would use the objects on the
surface of the ground for the same end.
as the grass, leaves, tree branches or
house projections. Moisture would then
be ever dripping. The occasional genial
rain, though at times lashed mp to a
biting storm Of sleet. would require to
give place to constant wetness on the
roads and grass.
Umbrellas would not be needed, but
india rubber protectors for the feet and
legs would be in constant requisition.
Even the irritable housekeeper, ever an
moved at the unaccOuntable appearance
of dust in rooms which she left for clean,
would prefer the old necessary evil in
this dry dust form than see the walls
dripping and the floor wet. - Good
WrrlS