298 MAGNUS ON THE EXPANSIVE FORCE OF STEAM. 
was the vapour, stood 1°65™™ higher than in the other. To 
this is to be added the pressure which the water exerted in 
this arm; its height amounted to 2°65™, its pressure was conse- 
quently equal to a column of mercury of 0°20™™, the expansive 
force of the vapour was consequently 1°85™™ less than that of 
the rarefied air, or = 320°41™™, 
The temperatures are referred to the absolute expansion of 
the air, and calculated from the indications of the air thermome- 
ter, according to the formula which I have given in the memoir 
on the expansion of air at high temperatures*, viz. retaining the 
symbols there selected : 
Hith—e_, 
eo 2 H+h—e 
oF H'+ hi—e 
fie ee 
H+h-—e 
in which © denotes the absolute expansion of the air expressed 
in degrees of the centesimal scale, 
H + 4 —e the elasticity of the air contained in the thermometer 
atiO°s 
H! + 4’ —e the elasticity of this air at the temperature 0, 
8 the expansion of the glass, and 
a the absolute expansion of the air for 1° of the centesimal scale 
(in that memoir this was represented by saa)" 
The correction y there applied is omitted because it has no per- 
ceptible influence for the temperatures now under consideration. 
For the temperature 100° C, the boiling-point of water under 
the pressure 760™™ + is taken differing from the former investiga- 
tion, where the boiling-point under the pressure of 28 Par. lin. 
is adopted. I have in the present instance preferred the metri- 
cal measure, in order to compare more easily my values with 
those calculated by M. Biot. Consequently, in the present case, 
the absolute expansion of the air from 0° — 100° or 100¢ is equal 
to the apparent expansion for the air contained in the ther- 
mometer from 0°— 160°C. 0°36394 resulted as the mean of seve- 
ral observations, whence we find § = 0:0000208}. In this man- 
ner the observations arranged in the following table were ob- 
tained, to which are appended the values calculated from the 
formula, which will be mentioned subsequently at p. 233. 
* Poggendorfft’s Annalen, vol. lvii. p. 191. 
+ In strictness it ought to have been about 759°52"". See Professor Miller’s 
Note at the end of this Memoir.—Eb. 
¢ Poggendorff’s Annalen, vol. ly. p. 17. 
