144 
PROFESSOR HUGH L. CALLENDAR OX 
Table XIV.—Comparison of Formulae. 
Temperature, 
Centigrade. 
Ludin, 1895. 
Barnes, 
Roy. Soc., 1900. 
B.A. Report, 
1899. 
Values of J. 
o 
0 
1-0084 
1-0084 
1-0094 
4-219 
5 
1-0051 
1-0055 
1-0054 
4-203 
10 
1-0026 
1-0031 
1-0027 
4-191 
15 
1-0009 
1-0012 
1-0011 
4-185 
20 
1-0000 
1-0000 
1-0000 
4-180 
25 
0-9998 
0-9991 
0-9992 
4-177 
30 
0-9999 
0-9986 
0-9987 
4-175 
35 
1-0006 
0-9984 
0-9983 
4-173 
40 
1-0017 
0-9984 
0-9982 
4-173 
45 
1-0030 
0-9986 
0•9983 
4-173 
50 
1-0046 
0-9991 
0-9987 
4-175 
55 
1-0063 
0-9999 
0-9992 
4-177 
60 
1-0079 
1-0001 
1-0000 
4-180 
65 
1-0094 
1-0006 
1-0008 
4-183 
70 
1-0109 
1-0013 
1-0016 
4-187 
75 
1-0123 
1-0020 
1 -0024 
4-190 
80 
1-0131 
1-0027 
1-0033 
4-194 
85 
1-0137 
1-0034 
1-0043 
4-198 
90 
1-0136 
1-0041 
1-0053 
4-202 
95 
1-0129 
1-0048 
1-0063 
4-206 
100 
1-0117 
1-0055 
1-0074 
4-211 
For the reasons already stated, the values in the above table are all expressed in 
terms of a unit at 20° C. for comparison, and are given to 1 part in 10,000 only. I am 
inclined to regard the values and formulae corresponding to the column headed “ B.A. 
Report, 1899,” as being the most probable. The corresponding values of J, the 
number of joules per calorie, are calculated assuming the value 4T80 at 20° C. 
(47.) Theoretical Discussion of the Variation of the Specific Heat. 
Clausius (‘ Mechanical Theory of Heat,’ p. 180, translation, 1879) has calculated 
the specific heat of water at constant volume C„ from that at constant pressure C p 
by means of the well-known equation, 
C„ = C, — T (dv/dT) p {dp/tin, = C, - T(dr/dT)f/(dv/dp) v . . ( 12 ). 
Taking Regnault’s values of C y „ Kopp’s values of the coefficients ol expansion, 
and Grassi’s values of the compressibility, Clausius finds the values, 
Temperature. 0° 25° 50° 
C„, at constant pressure . . 1'0000 l'OOlfi 1’0042 
C,, at constant volume . . . (P9995 (P9918 (P9684 
