PART iv. OCCASIONAL PHENOMENA. 41 



"the continual slight electrification of the air," usually 

 called atmospheric electricity, Professor Silvanus 

 Thompson, in his recently published work on Electricity 

 and Magnetism, writes at p. 262, " Our knowledge of 

 this important subject is still very imperfect. We do not 

 even know whether all the changes of the earth's electri- 

 fication, relatively to the air, are due to causes operating 

 above or below the earth's surface." And in his pre- 

 face, p. ix., where he is strong on the principle that 

 electricity is one not two, he also sets forth that the only 

 true and philosophical mode of regarding electricity 

 viz. as something which can neither be created nor 

 destroyed by man, only altered in its distribution, and to 

 which the grand doctrine of " Conservation of Energy " 

 is fully applicable had never been published in this 

 country until last year, and is in fact only now taking 

 shape among the leading natural philosophers of the 

 time. 



Again the eminent Professor Stokes, lecturing last 

 summer on Aurora at South Kensington in the cele- 

 brated series of solar physic lectures, dismisses its origin- 

 ation from either terrestrial magnetism or "earth currents" 

 as impossible on account of their feebleness. But let 

 him assume a supply of atmospheric electricity, such as 

 often is found there, to be at hand in the neighbourhood 

 of any auroral display, and he considers he has therein 

 what is abundantly powerful to account for all the visible 

 phenomena. In fact he goes on to consider that the 



