Year: 1878

London on Heat, Visible and lnvisi-
bic" was as interesting and instructive
! us the two which preceded 1T. He said
that they would proceed to examine
water in It's three forms, of solid, liquid
and vapor. First, as to its solid form
ice, to which savages very Justly gave
the name of water rock. 1t was law
almost, but not universal, that bodies
contracted with cold. Now, when
water was exposed to cold atmosphere,
the surface water contracted, became
heavier, and sunk to the bottom, the
warmer water below rising to the surface,
and sinking in it's turn as 1t grew chilled.
But by.and-by the descent of the cold
water ceased, slight film formed on
the surface, and if the cold continued,
solid cake of ice was produced, cover
ing the top and keeping in the warmth
which was in the lower water. The
cause of this would be examined later
on, but he wished now to call attention
to the fact that the ice was owing to the
formation of crystals. They had all
seen the beautiful figures which We're
produced when water tro2e on a pane OF
glass. He should like them to see the
process Of clystallzation in the act. He
would take piece OF glass, the surface
of which was perfectly clean, and would
wet it with solution of what is COM
monty called sal ammoniac, and then,
warming the glass to quicken the evap-
Grafton, he would throw magnificent
reflection upon the screen, and as the
solution froze on the glass, they would
see the crystalization Of the molecules
of water going on. CThe experience was
very beautiful one, and Prof Tyndall
said he had seen such crystals hundreds of
times, bat never without wonder.) He
would next decompose by the electric
current a solution of acetate of lead,
and they would see on the screen how
the atoms of lead would crystalize on
,he platinum wires, forming figures of
fronds and ferns. This experiment
was shown also with beautiful effect.
When snow fell in still atmosphere,
so that the molecules could exert their
force without disturbance, snow flowers
were formed, which are very beautiful.
photographs from drawings of snow
flowers were shown on the screen.) A
block of ice was a very different thing
from block of glass, being wonderfully
built up by the molecules of water, and
he would dissect plate of ice before
them. "a piece Of ice, cut parallel to
the surface Of freezing was placed before
the electric lamp, which showed ON the
screen the six petalled flower or crystal
of ice, with the vacuum spot in the cen
ter) He said that at certain point of
cooling, water ceased to contract, and re-
manned at the top, freezing at u temper
ature of 320 Fahrenheit. (The descent
of chilled water was shown.) He would
now show them the expansion of water
10y heat. (The experiment was shown,
water rising in tube from flask by
expansion.) If he put the flask Of
heated water into freezing mixture,
it would contract to certain point,
but then it would begin to expand again,
as water did when it froze; and if he
again heated the water it would first
contract, then expand; so that they
had water first expanding by heat, then
contracting by cold; then expanding by
cold, then contracting by heat, and then
expanding by heat. CThe experiment
was fully shown.) II he put into one
flask some ice and water, and into
another flask some waCer only, and APP
piled heat to both TASKS the temperature
of the one containing water would rise,
but the temperature of the other would
not be affected for a considerable time;
in the period required to hquify the ice
in the one flask, without any change Of
temperature, the water in the other
flask would boil, so that the heat which
in one case would raise the water to the
boiling point would in the other be con-
sumcd in melting the ice. Now, in the
latter case, what had become of the
heatl 1t used to be supposed that the
heat was hidden in the water; and when
water was boiled, and the temperature
stood at 2l2 degrees Fahrenheit, though |
heat was kept applied, it used to he sup
posed that the heat was bottled up in
the steam; and people called this heat
which was supposed to be so hidden, la
tent heat. But now it WAS known that
whenever IA substance was converted
from the solid to the liquid form, or
from the liquid form to vapor, there was