62 On the Relations of the Elastic Force, Density, and Temperature, 



A preliminary set of experiments, taken on the 26th of Sep- 

 tember 1861, the barometer 29*61 inches, with the air-pump 

 and large receiver, and a new barometer-gauge before it was 

 measured to allow for the capillary depression, gave results, con- 

 verted to Fahrenheit's degrees, as follows : — 



Height of mercury in the gauge ~\ i n# the air re-entering suddenly, the 1 9.q 

 above the level ) temperature rises f 



33 i) * i) 3} I ** 



„ „ o ,, „ iJ'U 



33 S> 4 » 33 lO'l 



These are nearly in arithmetic progression for condensations 

 in arithmetic progression, according to Poisson's law. On the 

 27th of September, with the capillary depression of the gauge 

 carefully allowed for, the following were obtained, the barometer 

 standing at 29 '88 inches, and the thermometer at 60° : — 



Height of mercury 

 in the gauge. 



Number of trials. 



Increase of tempe- 

 rature in Fahren- 

 heit's degrees. 



Approximate 

 condensations. 



inches. 

 6 



5 



4 



3 



2 



1 



7 

 3 

 3 

 3 

 3 

 3 



222 

 18-2 

 13-9 

 11-4 

 7-4 

 3-7 



ith 

 -i-th 



75 



TVth 



•^th 



The experiments differed only slightly amongst themselves, and, 

 with the exception of those where the height of the gauge was 

 4 inches, they form a very certain arithmetic progression in 

 accordance with M. Poisson's rule; but the absolute increase of 

 temperature is very little more than one-half what his expression 



209° 8 requires; for 8= P -^-=^- gives 6°-96 Fahrenheit, 



p oU 



whilst the observed increase of temperature was only 3 0, 7, 

 occurring in one second of time after the condensation had 

 taken place. 



The law of the increase of temperature being as the condensa- 

 tion, is the important point shown in these experiments, and 

 which the other methods did not show; whilst the time in which 

 it occurred may have been much less than one second, as exhi- 

 bited by the thermometer. 



