Mr. W. S. Jevons on the Forms of Clouds. 253 



ventures definitely to state how electricity can produce or modify 

 them. 



When we have a prospect of assigning other simpler forces as 

 the true causes of the forms of clouds, it is unphilosophical even 

 to mention electricity in conjunction with these. 



32. But, surely, meteorologists have strangely mistaken the 

 true functions of electricity in ever proposing it as a cause. 

 Sir J. Herschel expi-esses himself to this effect (Essays, &c., 

 p. 245) : — " Here also we have to deal with electricity as a third 

 element, but we strongly incline to the opinion, that its agency 

 as a meteorological cause, is exceedingly limited, indeed, that it 

 may be altogether left out of the account as productive of any 

 meteorological effects of importance on the great scale.'' 



Electricity has no place among the principles of meteorology ; 

 it is but an accidental or secondary effect, by which I mean one, 

 as it were, of a different order from its cause, and which does not 

 produce any appreciable reaction. 



One example will illustrate this position. It is always stated 

 in electrical treatises, that when the back of a common domestic 

 cat is smartly rubbed, crackling sparks of electricity will be 

 emitted. Friction is undoubtedly the cause, in this case, of the 

 electricity; but would any one be foolish enough to suppose that 

 electrical attraction was in any way the cause of your hand being 

 brought near the cat's back and rubbed upon it ? 



The sparks are a secondary effect of the force expended in 

 rubbing ; and although they may be said to contain a minute 

 amount of force under a very peculiar form, they can have no 

 appreciable reaction. Similarly, the atmospheric sparks are a 

 secondary effect of the friction of curi'ents of air, but the mecha- 

 nical force manifested in the whole discharges of a large thunder- 

 cloud must be almost infinitely small compared with the force 

 required to raise thousands of tons of water to the elevation of 

 the clouds, and to stir up the winds till their pressure amounts, 

 perhaps, to 10 lbs. on each square foot of opposing surface. 



33. Yet it may be well if I can offer any suggestion to recon- 

 cile the secondary effect in question, with the simple and funda- 

 mental causes whch I believe to operate in clouds. Possessing, 

 as I assume, a clear idea of the motions and changes which con- 

 stitute a cumulus, and therefore the thunder-cloud, which is 

 essentially a cumulus with a derivative and, as it were, organized 

 system of cirrus and stratus, I see no difficulty iu offering an ex- 

 planation which is at least plausible. My only fear is that it is 

 not original. 



Atmos))heric air almost always possesses a faint charge of elec- 

 tricity diffused through it, as the electric excitation is diffused 

 over the surface of the glass cylinder of the electrical machine. 



