of Edinburgh, Session 1879-80. 
545 
gas thermometer which we have now described may give even more 
accurate thermometry than Regnault’s constant-volume air thermo- 
meters, and it seems certain that it will be much more easily used 
in practice. 
We have only to remark here further that, if Boyle’s law were 
rigorously fulfilled, thermometry by the two methods would be 
identical, provided the scale in each case is graduated or calculated 
so as to make the numerical reckoning of the temperature agree at 
two points, — for example, 0° C. and 100° C. The very close agree- 
ment which Regnault found among his different gas thermometers 
and his air thermometers with air of different densities, and the 
close approach to rigorous fulfilment of Boyle’s law which he and 
other experimenters have ascertained to be presented by air and 
other gases used in his thermometers, through the ranges of density, 
pressure, and temperature at which they were used in these thermo- 
meters, renders it certain that in reality the difference between 
Regnault’s normal air thermometry and thermometry by our 
hydrogen gas constant-pressure thermometer must be exceedingly 
small. It is therefore satisfactory to know that for all practical 
purposes absolute temperature is to be obtained with very great 
accuracy from Begnault’s thermometric system by simply adding 273 
to his numbers for temperature on the centigrade scale. It is 
probable that at the temperatures of 270° or 300° C. (or 532 or 
573 absolute) the greatest deviation of temperature thus reckoned, 
from correct absolute temperature, is not more than half a degree. 
Monday, 3 d May 1880. 
Professor DOUGLAS MACLAGAU, Vice-President, 
in the Chair. 
KEITH PRIZE. 
The Chairman announced that the Council had awarded the 
Keith Prize, for the biennial period 1877-79, to Professor H. 
C. Eleeming Jenkin, for his Paper “ On the Application of 
Graphic Methods to the Determination of the Efficiency of 
Machinery,” published in the Society’s Transactions ; Part II. 
having appeared in the volume for 1877-78. 
3 x 
VOL. X. 
