Year: 1873

! S0c Gives IN ~ Much Heat 01 our
| Hand EMtts 1T . Ys rd's Dlstance.
| From the London Spectator.


! The Earl of R0sse has shown by ex-


periments that the moon not only re-.
fleets heat to the earth (which, of
course, must be the case), but that she
gives out heat by which she has been
herself warned. The distinction may
not perhaps appear clear at first sight
to every reader, but it may easily be
explained and illustrated. If on q
bright summers day we take q piece of
smooth, but not too we'll polished metal,
and by means of it reflect the suns
light upon the face, a sensation of heat
will be experienced; but if we wait
while so holding the metal until the
plate has become quite hot un.
der the solar rays, We shall
recognize q sensation of heat
from the near proximity of the
plate to the face, even when the plate
is so held as not to reflect sun heat.
We can in succession try, first, reflected
heat alone, before the metal has grown
hot; next, the heat which the metal
gives out Of itself when warmed by the
suns rays; and lastly, the two kinds
OF heat together, when the metal is
caused to reflect sun-heat, and also
(being held near the face) to give out a
sensible quantity of its own warmth.
What Lord Rosse has done has been to
show that the full moon sends earth
wards both kinds of heat; she reflects
solar heat just as she reflects solar
light 3; and she also gives out the heat
by which her own surface has been
warmed.


1t may perhaps occur to the reader to
inquire how much heat we actually ob-
tain from the full moon. There is a
simple way of viewing the matter. If
the full moon were exactly as hot as
boiling water, We should receive from
her just as much heat (leaving the ef-
feet Of our atmosphere ont of account)
az we should receive from . small
globe as hot as boiling water, and at
such distance as to look just a. large
as the moon does. Or disc of metal
would serve equally we'll. Now, the
experiment may be easily tried. A
bronze halfpenny is exactly one inch in
diameter, and as tho moons average
distance il about Ill times her own
diameter, a haIfpenny at distance of
Ill inches, or three yards and three
inches, looks just as large as the moon.
Now, let halfpenny be put in boiling
water for a while, so that it be-
comes as hot as the water; then that
coin taken quickly and set three yards
from the observer will give out, for
the few moments that its heat remains
appreciably that of boiling water, as
much heat to the observer as he re-
ceives from the full moon supposed to
be as hot as boiling water. Or globe
OF thin metal, an inch in diameter and
full of water at boiling-heat, would
serve as more constant artificial moon
in respect of heat supply. It need not
be thought remarkable, then, if the
heat given out by the full moon is not
easily measured, or even recognized.
Imagine how little the cold of win
ter's day would be relieved by the
presence, in a room not otherwise
warmed, of one-inch globe of boiling
water, three yards away !! And by the
way, we are here reminded of an eati-
mate by Prof. G. p. Smyth, resulting
from observations made on the moons
heat during his Teneriffe experiments.
He found the heat equal to that emit
ted by the hand at a distance of three
feet.