458 On the Potential Energy of Liquid Surfaces. 



from a diminution of temperature due to the great increase 

 of the liquid surface without the platinum sponge being wetted, 

 thanks to the layer of air which covers it ? But soon this air 

 is expelled ; and then a large surface is wetted by the liquid, 

 whence results a rise of temperature, and consequently a 

 current in the opposite direction and more energetic than the 

 first. 



V. Equations (1) and (2) appear to me to prove rigorously 

 that every change in the surface of a liquid gives rise to a 

 change of temperature, and, if the circuit is closed, to a ther- 

 moelectric current. From this point of view these equations 

 must he of capital importance in meterology. Indeed, if a 

 mere drop of water falling into a pond, and there losing the 

 whole of its original free surface, can produce, independently 

 of the action of gravity, a diminution of potential energy, and 

 consequently a heating, to w T hich corresponds a variation in 

 the electrical difference of the pond — if the smallest quantity 

 of vapour that rises from a liquid produces a diminution of 

 temperature and of electric difference, what powerful thermal 

 and electrical effects have we not to expect from those im- 

 mense variations of free surface in the waters that cover the 

 earth and in the vapours that rise into the atmosphere ? On 

 the one hand, the waters of the sea are submitted, owing to 

 the action of the sun, to continual evaporation, which causes 

 the thermal and electrical state of the earth to be incessantly 

 changing, and constantly develops in it thermoelectric cur- 

 rents ; and on the other, the enormous quantities of vapour 

 which rise into the atmosphere must there be subjected to in- 

 cessant variations in their surface of contact with the air, from 

 the state of extreme (I will say molecular) tenuity to that in 

 which, through sudden condensation, they produce prodigious 

 quantities of electricity and fall in torrents upon the surface 

 of the globe from which they were raised. Thus, then, on 

 the one hand would be found established the existence of a 

 constant source of thermoelectric currents circulating in the 

 earth ; and on the other we should recognize a permanent 

 cause of development of electricity in the atmospheric air, 

 and the explanation of the enormous electrical discharges 

 produced in tempests. 



I deem that the preceding considerations collectively suffice 

 to show the astonishing fecundity of the formula (1) ; only, 

 as I desire to confirm more and more the consequences above 

 indicated, and, if need be, to rectify them in certain points, 

 I here conclude my preliminary communication, reserving 

 for special memoirs the developments of the questions which 

 I have raised. 



