100 



5. The total mechanical force exerted by a volume of air while 

 expanding indefinitely is proportional to its G temperature. 



6. A given quantitj^ of air while expanding, under a constant 

 pressure, from one temperature to another, exerts a mechanical force 

 equivalent to one-third the difference of temperature ; and the quan- 

 tity of heat required to change the temperature of air under a con- 

 stant pressure, is four- thirds of that required to effect the same change 

 of temperature with a constant volume. 



The author concludes by observing that it is singular that these 

 simple and, he considers, important deductions from MM. Gay-Lussac 

 and Welter's experiments, have been overlooked by the eminent ma- 

 thematicians who have elaborately discussed this subject. The arti- 

 ficial position of the zero-point on the ordinary scales of temperature 

 may perhaps account for this by its tendency to confine our ideas. 

 Dalton's and Gay-Lussac's law of expansion seems imperatively to 

 have required that, in all computations having reference to gases and 

 vapours, the temperature should have been reckoned from the zero 

 of gaseous tension ; yet it has not been so ; and it is impossible to 

 avoid the conclusion, that if it had been otherwise, if no other tem- 

 perature but what we have had so often to refer to as the G tempe- 

 rature had been indicated in their analyses, we should have profited 

 more by their labours, and been further advanced in the science of 

 heat and elastic fluids. 



The Society then adjourned over the vacation to Thursday the 

 20th November, 1851. 



