On the Direct Determination of the Specific Heat of Gases. 341 



be conceived as occurring at considerable depths without the de- 

 velopment of a cavernous structure in the interior. Much of 

 this cavernous structure would doubtless communicate by means 

 of fissures with the surface, and thus there would be provided an 

 internal receptacle for the ocean, from the depths of which even 

 the burning sun of the long lunar day would be totally unable 

 to dislodge more than traces of aqueous vapour. Assuming the 

 solid mass of the moon to contract on cooling at the same rate 

 as granite, its refrigeration through only 180° F. would create 

 cellular space equal to nearly 14^ millions of cubic miles, which 

 would be more than sufficient to engulf the whole of the lunar 

 ocean, supposing it to bear the same proportion to the mass of 

 the moon as our own ocean bears to that of the earth. 



If such be the present condition of the moon, we can scarcely 

 avoid the conclusion that a liquid ocean can only exist upon the 

 surface of a planet, so long as the latter retains a high internal 

 temperature. The moon then becomes to us a prophetic pic- 

 ture of the ultimate fate which awaits our earth, when, deprived 

 of an external ocean and its axial rotation reduced to a rate 

 between monthly and annual*, it shall revolve round the sun 

 an arid and lifeless wilderness, each hemisphere alternately ex- 

 posed to the protracted glare of a cloudless sun and plunged into 

 the gloom of an arctic night. 



LIV. On a New Method for the Direct Determination of the 

 Specific Heat of Gases under Constant Volume. Bij C. K. 

 Akin, Esq.f 



SINCE the revival of the theory which considers heat as 

 Energy or vis viva due to molecular motions, the exact 

 knowledge, from direct experimental data, of the specific heats 

 of gases under constant volume, which alone of all similar 

 magnitudes represent what have been called real specific heats, 

 has become more than ever important. The methods hitherto 

 chiefly followed for the determination of the specific heats of 

 gases under constant volume are exceedingly indirect j and whilst 

 some of them, such as that of Dulong, involve hypotheses which 



* Mayer has proved that the action of the tides tends to arrest the mo- 

 tion of the earth upon its axis. And although the length of the terrestrial 

 day has not increased by the T1 ! \- u th part of a second since the time of Hip- 

 parchus, yet this fact obviously leaves untouched the conclusion to which 

 Mayer's reasoning leads. 



Since the above was written, Mr. James Croll has communicated to the 

 Philosophical Magazine (vol. xxvii. p. 285) an elaborate paper on this in- 

 fluence of the tides. 



f Communicated by the Author. 



