156 REPORT—1896. 
At the same time I quite acknowledge that the establishment of this unit 
will cause a considerable revolution in present thermal calculations which 
will be difficult to carry out, and it will therefore probably meet with 
energetic opposition from practical physicists and from technical men. 
Still, as I have already remarked, I should consider it a great step in 
advance if even the value of the equivalent of heat were established. 
6.—From Dr. Wiillner, Professor of Physics, Aachen, 
February 23, 1896. 
[TRANSLATION. ] 
I, also, have finally decided on determining the unit of heat by the 
work done, inasmuch as I have endeavoured to determine the work which 
is equivalent to the mean calorie measured by the ice calorimeter. 
I hope I made it evident that I am quite aware of the uncertainty of 
this method of calibration. I thus arrived at the value 4175'8 x 104, or, in 
whole numbers, 4176 x 104, which, according to Rowland, corresponds to the 
heat required to raise the unit weight of water through 1° C. at 22° C. 
of the air thermometer. 
I am, however, quite willing, if an agreement can be arrived at, to 
discard the always uncertain relation to the mean unit of heat, and to 
accept your proposed unit 42x 10°. The temperature 15°, at which the 
specific heat of water is then unity, is more convenient. The consequence 
of such an agreement will be that all thermal measurements in which 
absolute values are aimed at will be made with the water calorimeter, 
in which case it appears easier to experiment with temperatures about 
15°; also we are in better agreement as to the behaviour of water 
between 10° C. and 20° C., although, even then, there is not complete 
certainty. I should, for example, prefer to make the reductions at 15° 
entirely according to the observations of Rowland, as he has directly 
measured the equivalent of heat at these temperatures. Finally, as 
regards the designation of the new unit, I do not approve of giving it the 
name of a physicist ; also the name ‘therm’ is suitable for English 
physicists, but not for others. 
Why should we not simply preserve the name ‘thermal unit’? Or, if 
a distinctive name is used, then, approximating to the long-used ‘calorie,’ 
call the new unit a ‘calor.’ The definition would then be, ‘ A calor is the 
heat value of 41:89 x 10° ergs,’ and, until further notice, the calor will be 
equal to the amount of heat which will raise the unit mass of water 
at 15° through 1° C. 
No especial name has been given to the length of the mercury column 
which is equivalent to 1 ohm. In no case would I advocate the adoption 
of a second definition for the practical unit (besides ‘ Rowland,’ ‘ calor,’ 
or simply ‘thermal unit’), as that would lead to confusion. 
7.—From Dr. Boltzmann, Professor of Theoretical Physics, Vienna, 
November 26, 1895. 
The unit ought to be as simple as possible and capable of accurate 
determination, as all other qualities are of less importance. It would be 
simplest to choose the heat which raises the temperature from 10° to 11° C. 
In general I am in accord with all you say in your paper. The most 
