As the result of the brilliant researches of Rowland and of Mr
Griffiths on the variations of the specific heat of water, physicists
have decided to take as calorific standard the quantity of heat
necessary to raise a gramme of water from 15 deg. to 16 deg. C., the
temperature being measured by the scale of the hydrogen thermometer of
the International Bureau.
On the other hand, new determinations of the mechanical equivalent,
among which it is right to mention that of Mr. Ames, and a full
discussion as to the best results, have led to the adoption of the
number 4.187 to represent the number of ergs capable of producing the
unit of heat.
In practice, the measurement of a quantity of heat is very often
effected by means of the ice calorimeter, the use of which is
particularly simple and convenient. There is, therefore, a very
special interest in knowing exactly the melting-point of ice. M.
Leduc, who for several years has measured a great number of physical
constants with minute precautions and a remarkable sense of precision,
concludes, after a close discussion of the various results obtained,
that this heat is equal to 79.
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