of Air under Volume and under Pressure. 



using a tall jar, and pouring in more liquor till that in the gauge 

 reached its former level. However, it is easier and more accu- 

 rate in practice, to overlook those increments of volume, because 

 they will be proportional to the depressions themselves, and 

 therefore, the ratio of these depressions, which gives the thing 

 wanted, is not altered by this circumstance. For the same rea- 

 son, it is better to neglect any change in the height of the liquid 

 in the cistern, and only to observe its height when the air-vessel 

 is open. 



As an error might have been introduced by allowing the li- 

 quid in the tube to spring up and displace a portion of the air 

 it contained, or at least to render the volume uncertain by its 

 undulations, a cork was struck in it, immediately above the com- 

 mon level. It was not so tight as to prevent the passage of air, 

 but it operated as a sufficient check to the rise of the denser 

 fluid. Every other precaution I could think of was attended 

 to, and the mean of many experiments with this apparatus gave 

 the ratio of the specific heat of air under a constant volume, to 

 that under a constant pressure, as 1 to 1.334, which is so near- 

 ly as 3 to 4, that I am inclined to consider this the true value. 

 However, I intend to repeat these experiments, and to prove 

 them by a different process. 



The ratio of 3 to 4 does not completely bear out the amend- 

 ment proposed on the Newtonian theory of sound, by the Mar- 

 quis La Place. But a complete theory ought to account for the 

 almost absolute control which wind exercises over the intensity/ 

 of sound. I have often thought that both the intensity and the 

 excess in the experimental over the theoretical velocity, are con- 

 nected with the reaction of the earth's surface. As an illustra- 

 tion of this, sound is well known to be rendered more intense, 

 by passing along the face of a wall or precipice ; and very likely 

 it is at same time accelerated. 



From the experiments of MM. Desormes and Clement, the 

 ratio of the specific heat of air under a constant volume, is to 

 that under a constant pressure, as 1 to 1.354; and from those 

 of MM. Gay Lussac and Welter as 1 to 1.375. The fractional 

 part of both approaches to J, and Mr Ivory has adopted this, 

 and suggested a reason why it should be the true value *. By 



* Phil. Mag. Ixvi. 9. 



