562 MR W. J. M. RANKINE 
To enable others to judge of the accuracy of this result, I shall now explain 
the method by which it was obtained, annexing a copy of the diagram used. 
Let E denote the mean rate of increase, per degree, between the freezing and 
boiling points, of the pressure of a gas whose volume is maintained constant. 
Then the reciprocal of this coefficient, 2 > is an approximation to the number of 
degrees below the freezing point, at which the absolute zero is situated. 
The experimental data in the following table were copied from the memoirs 
of M. ReaNnauut on the Expansion of Gases. The numbers in the first column 
designate the series of experiments. The second column contains the pressures 
of the gases at the freezing point. The third column contains the mean coefficients 
of increase of pressure per centigrade degree, between 0° and 100° centigrade. 
The fourth column contains the reciprocals of those coefficients, with the negative 
sign, being approximate positions of the absolute zero, in centigrade degrees, below 
the temperature of melting ice. The gases employed were atmospheric air and 
carbonic acid. 



Precnue at_| Coeiient of n- AEpresipatepntion 
No, | Centigrade ern of Baty] centigrade degree 
Atmospheres. =. =5 
CARBONIC ACID. 
1. | 0:9980 | 0-0036856 —271:33 
2.| 1:1857 | 0-0036943 —270-63 
3. | 22931 | 0-0037523 —266°50 
4.| 47225 | 0-0038598 — 259-08 
ATMOSPHERIC AIR. 
1.| 01444 | 0:0036482 —274-11 
2.| 0:2294 | 0-0036513 —273:88 
3. | 03501 | 0-0036542 —273-66 
4.| 04930 | 0-0036587 —273°32 
5. | 0-4937 | 0-0036572 —273:43 
6. | 1-0000 | 00036650 —272:85 
7.| 22084 | 0-0036760 — 272-03 
8. | 22270 | 0:0036800 —271-74 
9.| 28213 | 0-0036894 —271:05 
10.| 48100 | 0:0037091 —269°61 



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