investigating the Specijic Heats of the Gases. 5 



This indispensable datum Dulong deduced from certain experiments with a 

 flutc'like pipe or tube, blown through by the different gases, from which, by the 

 application of the theory of wind instruments, he was enabled to calculate the 

 length of a single vibration, and the number performed in a given time, for seve- 

 ral of the elastic fluids. 



The velocities thus obtained were then divided by their values as given by 

 Newton's formula, and the quotients squared necessarily represented, as has been 



already shown, 1-| — , or the relation for each gas between its specific heat under 



a constant volume and a constant pressure. The following are the results to 

 which he was thus conducted :— 



A glance at the first column of this table would appear sufficient to justify the 

 conclusion, that the mixed number which represents the relation in question, is 

 the same for all the simple gases, but that this law does not extend to those of a 

 compound nature, with the exception of carbonic oxide. 



If b have the same value for all gases, simple or compound, or, as is indeed 

 extremely probable, if all, in undergoing the same degree of compression, give 



out the same amount of heat, a, must vary reciprocally as -, that is the specific 



heats, under a constant volume, will vary reciprocally, as the fractions in column 

 (1.) Upon this hypothesis, values of a, the specific heat under a constant vo- 

 lume, have been calculated for each gas, that of air being represented by unity, 

 and are set down in column (2). In column (3) we have values of a-\-b, the 

 specific heat, under a constant pressure, which are obtained by multiplying the 

 corresponding numbers, in columns (1) and (2), and dividing all the products by 



