228 POPULAR LECTURES AND .IMPRESSES. 



shows us unusually great disturbances not only 

 when there arc aurora and variations of terrestrial 

 magnetism, but when the atmospheric electricity 

 is in a disturbed .state. That it should be so 

 electricians here present will readily understand. 

 They will understand when they consider the 

 change of electrification of the earth's surface which 

 a lightning discharge necessarily produces. 



I fear I might occupy too much of your time, 

 or else I would just like to say a word or two 

 upon atmospheric electricity, and to call your 

 attention to the* quantitative relations which 

 questions in connection with this subject bear to 

 those of ordinary earth currents and the phe- 

 nomena of terrestrial magnetism. In fair weather 

 the surface of the earth is always, in these countries 

 at all events, found negatively electrified. Now 

 the limitation to these countries that I have made 

 suggests a point for the practical telegraphists all 

 over the world. Let us know whether it is only 

 in Kngland, I 'Vance, and Italy that in fine weather 

 the earth's surface is negatively electrified. The 

 only case of exception on record to this statement 



