ELECTRICAL STANDARDS. 161 
14.—Irom Professor EB. L. Nichols, Professor of Physics, Cornell 
University, Ithaca, U.S.A.. January 12, 1896. 
The suggestion of defining the heat units by means of the melting of ice 
strikes me so favourably that, in spite of the difficulties which have hitherto 
been found in determining the precise heat of fusion, I am considering the 
question of the redetermination by new methods with a view of finding 
whether one can obtain a sufficient degree of accuracy to warrant the 
adoption of the heat of fusion of water as the basis for thermal measure- 
ment. 
15.—From Professor Rowland, Professor of Physics, Johns Hopkins 
University, Baltimore, U.S.A., December 15, 1895. 
As to the standard for heat measurement, it is to be considered from 
both a theoretical as well as a practical standpoint. 
The ideal theoretical unit would be that quantity of heat necessary to 
melt one gramme of ice. This is independent of any system of ther- 
mometry, and presents to our minds the idea of quantity of heat indepen- 
dent of temperature. 
Thus the system of thermometry would have no connection whatever 
with the heat unit, and the first law of thermodynamics would stand, as it 
should, entirely independent of the second. 
The idea of a quantity of heat at a high temperature being very dif- 
ferent from the same quantity at a low temperature would then be easy 
and simple. Likewise we could treat thermodynamics without any refer 
ence to temperature until we came to the second law, which would then 
introduce temperature and the way of measuring it. 
From a practical standpoint, however, the unit depending on the 
specific heat of water is at present certainly the most convenient. It has 
been the one mostly used, and its value is well known in terms of energy. 
Furthermore, the establishment of institutions where it 7s said thermo- 
meters can be compared with a standard renders the unit very available 
in practice. In other words, this unit is a better practical one at pre- 
sent. Iam very sorry this is so, because it is a very poor theoretical one 
indeed. 
But as we can write our text-books as we please, I suppose that it is 
best to accept the most practical unit. This I conceive to be the heat 
required to raise a gramme of water 1° C. on the hydrogen thermometer 
at 20° C. 
I take 20° because in ordinary thermometry the room is usually about 
this temperature, and no reduction will be necessary. However, 15° 
would not be inconvenient, or 10° to 20°. 
As I write these words I have a feeling that I may be wrong. Why 
should we continue to teach in our text-books that heat has anything to 
do with temperature? It is decidedly wrong, and if I ever write a text- 
book I shall probably use the ice unit. But if I ever write a scientific 
paper of an experimental nature I shall probably use the other unit. 
1896. M 
