246 Intelligence and Miscellaneous Articles. 



while the steam is positive. In the machine there is a box full of 

 water to cool the tubes through which the steam emerges. Hence 

 before the steam escapes it begins to condense, and thus passes out 

 mixed with vesicles of water. This is a necessary condition. 



According to Faraday's experiments the passage of dry steam or 

 of a current of dry air does not liberate electricity, while a current 

 of moist air gives the same result as Armstrong's machine, but to a 

 less extent. M. Spring, it is true, found that the friction of dry air 

 against a copper sphere gave a little electricity, but a quantity far 

 less than in Faraday's experiment. On the other hand, it has been 

 shown by numerous experiments that the mere evaporation of 

 water, even when acidulated, does not produce electricity. But in 

 evaporation produced by wind there is friction, and in this mecha- 

 nical ivork the desired cause is to be sought. 



The wind in graziug the surface of the sea carries with it the 

 aqueous particles of the crest of the waves, which here play the 

 part of the comb in Armstrong's machine. The roughnesses on 

 the surface of the soil play the same part when a moist wind 

 blows over them. These particles of water retain their electricity, 

 and rising in the atmosphere form clouds, and as electricity passes 

 to the surface of bodies, they tend to spread over the highest atmo- 

 spheric surfaces ; and I hold, with M. Faye, that the cirrus must 

 retain great part of this electricity. 



That being admitted, it may be conceived that a cloud is elec- 

 trified if formed in the conditions just cited. It would not be the 

 case with a cloud formed by mere vapours rising in the air in the 

 morning. 



But to produce lightning there must be a discharge between the 

 cloud and another point, the earth or cloud, such that the dif- 

 ference of potential between the point and the cloud, at the 

 moment in question, is sufficient to produce the lightning. 



But the distance across which the spark passes depends on the 

 electric pressure and on the mechanical resistance which the medium 

 presents to the discharge. This pressure varies with the square 

 of the potential of the cloud, its form, its surface, the charge of 

 the cloud, and its distance from the point in question. 



But the potential energy of a cloud depends on its form, its 

 surface, and its temperature. When this cloud originally elec- 

 trified undergoes any change whatever (condensation, congelation 

 of aqueous vesicles, &c), it absorbs a certain amount of energy, 

 which should be found in the form of an increase of potential 

 energy. 



This consequence results from the principle of the conservation 

 of energy, and from Carnot's principle, from which Lippmann has 

 deduced such remarkable results. 



If, then, we suppose that the charge of the cloud remains con- 

 stant for a certain time, condensation or lowering of temperature 

 will increase the potential of the mass. 



During a storm, it is very exceptional when there are no elec- 

 trical manifestations. The abundant condensation then observed is 



