Circumstances under 'which Steam developes Electricity/. 267 



the minute vesicles may be very easily distinguished from 

 water globules passing at the same time through the field of 

 the microscope, the former disappearing when coming in con- 

 tact with each other, the latter uniting in one larger globule. 



M. Fresnel considered the theory of Saussure as Inadmis- 

 sible, because the air surrounding the small vesicles must be 

 in a state near saturation, and therefore he thought it was 

 scarcely possible that the envelope of these little globules could 

 be of an equal or lesser density than the air in which the clouds 

 are suspended. Further, he considered the swiftness of their 

 movement entirely irreconcilable with their vesicular state, 

 as the friction caused by such movement through the air would 

 soon set them at rest. Finally, he explains, as the air in the 

 vesicles must be in a state of condensation, as it has to resist 

 the tendency of the water molecules to unite themselves in 

 a drop, the globule would finally disappear, as a soap bub- 

 ble will swiftly diminish and disappear when the tube on which 

 it is suspended is removed from the mouth. But this latter 

 case only takes place when the film forming the soap bubble 

 is very thick, viz. in the beginning of its formation, and can 

 possiblj/ only occur when the bubble is joined to a tube, which 

 with the vesicles in the cloud is certainly never the case; 

 but when the bubble is once formed, every child knows that 

 it will stand till evaporation or concussion causes it to burst. 



The rapid movement of the small vesicles of water is for 

 the greatest part attributable to currents of air; and as there- 

 fore their velocity is equal to that of the molecules of the air, 

 no possible friction and loss of velocity can arise from this 

 circumstance. 



In further considering the equilibrium of the cloud, we 

 must not only bear in mind the single vesicles as such, but 

 the single vesicle surrounded of course by an atmosphere of 

 air and water-gas united to one substantial body, viz. the 

 cloud, and forming itself by exerting forces within, as molecules 

 of water when at liberty form and arrange themselves into a 

 shape where their mutual attractive forces are in a state of 

 perfect equilibrium. Besides, the surrounding air, as long as 

 the cloud swims in it, can only be in a state of saturation on 

 one part and in contact with the cloud. When the entire 

 air between the earth and the clouds is near saturation, the 

 clouds begin to decompose and discharge water. 



Fresnel assumes that clouds consist of minute solid globules 

 of water, and as the air, in their intervals and therefore in 

 contact with the globules, is easier to be heated by radiation 

 than air not in contact with solid or liquid bodies, he ex- 

 plains, that this air between the water globules is of a much 



