512 
Mr. Lubbock on the Heat of Vapours 
= _ J2'0651059] ^ 
1-17602 ’ 
and if ^ be the density of steam, the relative volume 
q p — 1-17602} 
f {^'*013^ — 1-17602}' 
In order to ascertain how far the new expression here given for 
T represents the totality of the observations, 1 have calculated the 
temperatures corresponding to all the observed pressures in the ob- 
servations of Arago and Dulong, and the results are exhibited in 
the following table. 
Pressure in 
atmospheres. 
Temperature. 
Error of tem- 
perature cal- 
culated by 
Lubbock. 
Fahr. 
Observed. 
Calculated. 
Merc, therm. 
Cent. 
Merc, therm. 
Fahr. 
Air therm. 
Fahr. 
Air therm. 
Fahr. 
2-1400 
123-7 
251-66 
25 ° 3-6 
25 ° 2-8 
~°8 
2-8705 
133-3 
271-94 
270-4 
270-1 
- -3 
4-5735 
149-7 
301-46 
299-2 
299-4 
+ •2 
6-4977 
163-4 
326-12 
323-0 
323-2 
+ •2 
7-3755 
168-5 
335-30 
331-9 
332-3 
+ •4 
11-6320 
188-5 
371-30 
366 - 7 * 
366-7 
0 
17-1850 
206-8 
404-24 
398-6 
398-9 
4- -3 
17-2850 
207-4 
405-32 
399-5 
399-4 
-•1 
18-5040 
210-5 
410-90 
404-9 
405-3 
+ -4 
21-5550 
218-4 
425-12 
418-5 
418-8 
+ •3 
23-9340 
224-15 
435-47 
428 - 4 * 
428-5 
+ •1 
The observations marked with an asterisk were employed in de- 
termining the constants. 
The error of the temperature calculated by the formula adopted 
by Arago and Dulong corresponding to the first observation is 
— *73 cent, or — 1°*3 of Fahr. I have no doubt that the observed 
temperature is in excess, and the agreement with the rest of the 
observations is so complete, that within this range of temperature 
the formula may, I think, be considered as exactly representing the 
phenomena. The errors of the temperatures, calculated by the 
various empirical expressions which have been hitherto proposed, 
are much greater, as may be seen in the table of Dulong and Arago. 
The following observations are those of Southern, given in p. 172, 
vol. ii., of Dr. Robison’s Mechanical Philosophy. 
