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tlio instrument would be impracticable to me, without the
improvement devised by Schuller and Wartha, viz. to
immerse the calorimeter in a vessel containing ice and pure
water at 0°. Still the advantage of this arrangement is not
to prevent variations in the position of the mercury index of
the instrument, but to make them quite regular.
The variations are declared by some physicists to depend
upon the vacillations of the atmospheric pressure, which
lowers or raises the melting point of the ice, but I dare say
from long experience, that the movement of the mercury
column is in some way .influenced by the temperature of the
air in the room, but is wholly independent of the barometric
variations. The real cause of the unsteadiness of the index
seem* to me to lie in the impurities absorbed by the water,
which has been kept boiling for almost an hour in the glass
reservoir by the filling of the instrument. Thus the ice will
bo exactly in the same condition as the sample II in the
above tables, viz. it will possess no absolutely fixed volume .just
below its melting point. The specific volume of the ice in the
instrument will thus correspond to some point of the sloping
branch of the curve 11, see plate 22, between—O’.os and 0°. Now
suppose the water in the external vessel to be either a little
purer than that of the calorimeter or vice versa. In the
former case its temperature, i. e. its melting point will be
situated a few thousandths of a centigrade higher, and the
volume of the ice in the calorimeter will move downwards
on the branch of the curve in the attempt to gain the
temperature of the surrounding medium. Then the index will
move slowly backwards, in the other case the coordinate of
specific volume of the ice will move upwards on «the sloping
branch, and the index of the seal e-tube will march forward.
1 think we could diminish this inconvenience by filling the
scrupulously cleansed calorimeter with repeatedly distilled
water and by confining the boiling operation to the least
possible time.
In studying the phenomena of the movement of glaciers,
we of course must acknowledge the powerful action of
pressure, but we will do well also to bear in mind, that an increase
of pressure, equal to the weight of a vertical column of ice
of 400 feet, is required only in order to make the melting
1 Stilt t cannot dispute the possibility of the hypothesis upheld by my
former companion, Professor Nilson, viz. that the contraction of the glass
reservoir may have something to do with these variations.
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