a i. en eee 
ELECTRICAL STANDARDS. 153 
Most of the writers wish to see some multiple of the erg adopted as 
the theoretical unit, but there are differences of opinion as to the mul- 
tiple to be chosen, 
Thus, Professors Dorn and Wiillner, Dr. Chappuis, and Professor Ames 
would prefer 42 x 10° ergs. Professor Ostwald, Professor Olszewski and 
his colleagues, and Professor Callendar suggest 10’ ergs. Professor Planck 
and M. Le Chatelier suggest 10% ergs, or in the case of the latter, as an 
alternative, 5 x 107. 
Professors Rowland and Nichols consider the ice unit as theoretically 
best ; the latter, however, would be willing to adopt 42 x 10° ergs as the 
theoretical unit, while Professor Rowland writes: ‘From a practical stand- 
point, however, the unit depending on the specific heat of water is cer- 
tainly the most convenient. It has been the one mostly used, and its 
value is well known in terms of energy.’ 
There is fairly general agreement in the view that as a practical unit 
the heat required to raise 1 gramme of water 1° C. at some fixed tempera- 
ture must be taken, but views differ as to the temperature which it is 
most convenient to choose. 
Mr. Griffiths suggested the nitrogen thermometer as the standard 
of temperature. The French physicists agree in the opinion that the 
hydrogen thermometer should be adopted, and reasons are given for this 
in the letters of M. Guillaume and M. Chappuis. The Committee concur 
in this view. 
The Committee are of opinion that Mr. Griffiths’ paper, and the 
replies received by him, show clearly that it is desirable to come to an 
agreement as to the definition of the unit of heat. 
They understand that a Committee of the French Physical Society have 
the question at present under consideration, and they hope it may be 
possible for the Electrical Standards Committee of the British Association 
to co-operate with this Committee and with representatives of other foreign 
countries in the matter. 
The Standards Committee have provisionally approved the following 
propositions, with the view of opening international discussion of the 
question. They propose to send the propositions to representative bodies 
throughout the world, with a letter stating that they have been provisionally 
approved, inviting further discussion, and asking those bodies to take the 
steps which seem to them most desirable in order to secure international 
agreement on the matter. 
Proposition I.—For many purposes heat is most conveniently 
measured in units of energy, and the theoretical C.G.S. unit of heat is 
lerg. The name Joule has been given by the Electrical Standards 
Committee to 107 ergs, 
For many practical purposes heat will continue to be measured 
in terms of the heat required to raise a measured mass of water through 
a definite range of temperature. 
If the mass of water be 1 gramme, and the range of temperature 1° C. 
of the hydrogen thermometer from 9°-5 C. to 10°-5 C. of the scale of that 
thermometer, then, according to the best of the existing determinations, 
the amount of heat required is 4:2 Joules. 
It will, therefore, be convenient to fix upon this number of Joules as a 
secondary unit of heat. 
This secondary thermal unit may be called a ‘Calorie.’ 
