OF TELE LATE ME. WILLIAM STURGEON. 75 



fluid around it, and thus produces an electrical wave which, 

 in some instances, reaches to great distances. 



Mr. Sturgeon noticed that thunderstorms are the most 

 violent when they occur over wet ground or water, owing to 

 the facility with which such a surface can he charged by the 

 inductive influence of electrified clouds; and also that elec- 

 trical storms generally travel in the direction of rivers or 

 along narrow tracts of wet ground. In his description of the 

 thunderstorm which occurred near Manchester on the 16th 

 July, 1850, he made an observation which was probably more 

 remarkable than any that had been previously made in at- 

 mospheric electricity. This consisted in the determination of 

 the time of a lightning discharge by means of the vibrations 

 of a pendulum ; the streams of electric fluid being visible in 

 some cases as long as a second and a-half. Mr. Clare and 

 others, including myself, who witnessed the same pheno- 

 menon from different points of view, coincided in remarking 

 that these streams of electric fluid took up a very sensible 

 time, and that the motion of electricity along them was ap- 

 parent. This extraordinary and magnificent spectacle seems 

 to have been owing to the great elevation at which the light- 

 ning was playing, where the rarefaction of the air would pro- 

 bably cause it to assume some of the characteristics of the 

 aurora borealis. 



Mr. Sturgeon does not appear to have embraced any theory 

 of the cause of thunderstorms. I may, however, remark, that 

 after the discovery by Faraday that the enormous evolution 

 of electricity in Armstrong's hydro-electrical apparatus is 

 owing to the friction of particles of water and air, it is pro- 

 bable that the electricity of the thunder-cloud arises from the 

 friction of the particles of water or ice of which it is com- 

 posed, or which are falling from it, against the cold non- 

 conducting air which exists at a high altitude. 



The aurora borealis was a phenomenon in which Mr. Stur- 

 geon took a great deal of interest. His observations of this 



