Saint Mary's beacon. [volume] (Leonard Town, Md.) 1867-1983, 1910-01-13

when the weather ~ not too cold?
Why do our skates "bite" or ,ate
hold OF the ice batter when is tenn
pera'ure is no, far below the f-aez
ing point? The exolsna,ion OF this
simple and uDiversa.ly re 2 liz d
fact will enable Us aiso TO sss tae
reason for arother. the truth Of
which is recognized ny every school
boy, ramely that STOW will pack
better into suowbal:s when nearly
81 its melting point.
The explanation ofbo,h these facts
lies in an almost unhiue property OF
water. or rasher i1ss whieh causes
il TO melt or tend 10 melt when pres
sure is applied to it. When the
pressure is relieved. il il is still be-
low its normal fire ezi ng temperature.
it at once solidi6eS again
This property is beautifully illus
trated in familiar experiment j.
which large cake Of ice is used.
supported at each end II a loop Of
fine wire is passed round it and o
weight attached TO the end, i, will
soon be noted that the wire is slow
ly cutting it's way through the ice,
but curiously enough without caus-
ing any division OF the cake. For
the ice is melted into water by the
pressure directly beneath the wire.
which water at once freezes into
ice again above the wire, so that
perhaps after an hours time the
wire will have cut it's wsv comp'e,
'elv through the cake, leaving II,
however. as solid and whole as
ever.
In the case Of the skater, then,
the weight OF his body carried on a
narrow skate may produce a pres
sure on the ice sufficiently great 10
melt small groove under the edge
OF the runner. This enables IL to
take hold of the ice more readily,
and furthe rmore the water acts as a
lubricant on the ice and makes II
slippery. Stree conside able pres
sure is necessary TO pro luce melt
ing even when the temperature is
only a degree or so below the nor
NAL melting point, tbs effect will
not take place on a very cold dav;
for, as is we'll knows, very cold ice
is not slippery The same explana-
tion holds for snowballs; but the
pressure Developed in this case is
much less. so that melting enough
to pack" we'll will not toccurunl-SS
the snow is nearly warm ough to
melt, ANYWAY.
This effect Is uoted on a grand
scale in the case of glaciers. which
flow slowly down mountain
side much as il ice Was q viscous
fluid. The great pressure develop
ed along the bottom a well as az the
turns and other points Causes a
slight melting, which is immedia
tely followed by freezing again as
soon as the pressure is relieved.
This enables the Ice to adapt itself
to the shape OF the va ley as it pro
ceeds on its way.
Ice is one OF the few substances
that show this effect OF melting un-
der pressure. and it does so b. cause
Of the fact that water expands on
freezing. The great majDrity of
substances contract on solidifying.
and hence would show the reverse
effect; that is, pressure appi ed to
them in the molten state would tend
TO cause solidifcation.
This is one reason for believing
that the Interior OF our earth as a
whole is solid rather than molten;
for while we believe that the tenn
perature OF the interior may be
much more than enough TO melt roc K
under ordinary conditi0ns.-snd in
deed volcanoes show that there is
plenty Of molten rock not SO very
far below the surfAce,-the eno--
nous pressurss that exist deep
down in the earth are enough 20
keep the material in a solid condi-