ELECTRICAL STANDARDS. 163 
necessary to express the author’s data in absolute measure, except that 
for the mere purposes of comparison one datum—the dynamical equivalent 
at one specified temperature—is not actually required. At the same time 
the comparison of data is in no way vitiated by the use of some number 
(for the present a conventional one), in order to convert a result from 
some definite gramme-degree-unit to Joules. 
An examination of the tables of thermal data with a view to expressing 
the results in Joules furnishes, therefore, a very effective test of the com- 
parability of the results obtained by different observers for the same 
thermal constants, and, moreover, the difficulties to be met with in making 
the reduction to Joules give the best indication of the points which must 
be settled before the results of thermal measurement can be regarded as 
final. To carry out such an examination completely, using numbers for 
reduction that can only be regarded as provisional, would be an unneces- 
sary labour, but a few selected instances may help to exhibit some of the 
uncertainties which might reasonably be expected to disappear if ob- 
servers once recognised the desirability of expressing all thermal mea- 
surements in Joules, or in some accepted equivalent. 
As an example, I have computed the total heat of water at various 
temperatures as determined experimentally. I have used Rowland’s num- 
bers for lower temperatures, and have recomputed Regnault’s experiments, 
accepting Table I. (computed from Rowland) as correct. 
I think it might be possible to find data enough to recompute some 
others, e.g., the latent heat of steam at 100°, the specific heat of air at 
constant pressure, which, by the way, is almost exactly a Joule. The 
labour is, however, very considerable, and it might be abbreviated (for the 
Committee) if those who are or have recently been engaged in thermal 
measurements would supply the Committee with the results of their own 
observations reduced to Joules and thermometric units. 
Taste I.—Total Heat of Water at Various Temperatures of the scale of the 
Hydrogen Thermometer between O° and 36°, expressed in Joules 
(Rowland’s Experiments). 
| Total Heat in Jou'es i T Total Heat in Joules 
T _ between 0° and T° I} | between 0° and T° 
o fe} 
5 21-044! | 21 88°144 
6 25:°254 | a, 92-321 } 
? 29°462 23 96-496 
8 33°668 | 24 100671 
9 37°871 25 104°844 
10 42-072 | 26 109-017 } 
1l 46271 . 27 113°188 
12 50-468 | 28 117-359 | 
13 54663 29 121°530 
14 58°856 30 125-700 
15 63:046 BL 129-871 
16 67-234 32 134-042 
17 F 71:420 | 33 138-214 
18 75604 34 142-386 
19 T9786 35 146°558 | 
20 83:°966 36 150°731 
' The total neat between 0° and 41° is obtained by extrapolation from Rowland’s 
numbers. 
M2 
