158 REPORT—1896. 
Vol. VI.) in the pamphlet on thermometry of precision by M. Guillaume, 
as well as in Landolt and Bornstein’s physical tables, 2nd edition, p. 93. 
Also a great number of physicists have adopted the decision of the 
International Committee of the Poids et Mesures to take, as the normal 
seale of temperature, that of the hydrogen thermometer at constant 
volume. 
10.—From Professor Le Chatelier, School of Mines, Paris. 
[TRANSLATION. | 
. . . I should like the thermal unit to be a number of ergs chosen 
arbitrarily ; either 10° ergs, or, in order to approach more nearly to the 
present unit, 5 x 10’ ergs. Then; as practical unit, I should like two : 
(1) A unit, of precision analogous to the ohm, which should be the quantity 
of heat yielded by a given mass of mercury in passing from one state to 
another, the states being defined by volume or electrical conductivity. 
(2) The present unit should be the specific heat of water at 15°. 
The use of water is indispensable for current researches, but it appears 
to me very doubtful for researches of precision. 
It is supposed that the condition of water and, consequently, its internal 
energy are completely determined when the pressure and temperature are 
ascertained. Now, nothing is less probable. Since Ramsay’s researches, 
we know decisively that water is formed of a mixture of molecules at 
various degrees of association ; it is a system in equilibrium. The state of 
equilibrium of analogous systems is in theory eutirely defined when the 
pressure and temperature are known. But in practice the state of 
equilibrium is only attained with an extreme slowness, and sometimes it is 
never reached. The lower the temperature, the more serious are those 
delays in reaching the state of equilibrium. It is therefore possible that 
the specific heat of water varies with the temperature, and that it differs 
according to whether the initial temperature of the experiment has been 
reached when ascending or descending. 
11.—From Dr, Guillaume, Bureau International des Poids 
et Mesures, Sevres, November 19, 1895. 
[TRANSLATION. | 
I believe that if the French Committee adopt your proposal as to the 
fixing of the new unit, they will declare themselves still more decidedly 
in favour of the name which you have given them, as it has already been 
proposed here to name ‘therm’ the equivalent of heat of the erg or of one 
of its decimal multiples. 
I do not think, in return, that we could agree with you as to the scale 
of the nitrogen thermometer. There appears to be no doubt that the 
hydrogen thermometer gives a scale extremely like the thermo-dynamic, and 
that it is, at all events, the most analogous we can have. Sooner or Jater 
it will be necessary to adopt the thermo-dynamic scale, and it is well 
to now approach to it as nearly as possible. 
Besides, this scale is one of a certain small number of units on whicha 
legal authority has been conferred. It is now included in the decisions 
arrived at by the International Committee of Weights and Measures, 
which a certain number of States have introduced into their legislation. 
In itself the thing is actually of little importance ; but it becomes more’ 
