128 Mr. J. P. Joule on a remarkable appearance of Lightning. 



the thunder, I consider that their general elevation from the 

 surface of the earth must have been at least 2>\ miles. 



The diverging form arose no doubt from the extensive ne- 

 gative surface presented by the clouds, 

 and may be imitated on a small scale 

 by filling a glass jar with water and 

 using it as a Leyden phial. If such 

 a jar be discharged by bringing one 

 ball of the discharging rod towards 

 the exterior glass surface, the other 

 ball being in connexion with the 

 water, the spark will, in restoring the 

 electrical equilibrium, diverge over 

 the whole glass surface. 



Another remarkable feature in the 

 lightning was the sensible time of 



its travelling towards the spectator. The main streams of 

 light were always formed before the diverging sparks; and 

 when formed, remained steady for an appreciable time, until 

 the whole disappeared together. My brothers, Messrs. Ben- 

 jamin and John Joule, who observed the lightning two miles 

 westward of my station, formed exactly the same impression 

 of its character; and in addition, the latter and several other 

 parties were witnesses of a phenomenon, which, if owing to 

 the electrical state of the atmosphere, was, I believe, without 

 a recorded precedent. 



At half-past 8 o'clock a bright red light appeared among 

 the clouds, bearing nearly due south, and having an elevation 

 of about 30° above the horizon. It appeared as if the sun 

 were behind a cloud illuminating its edges strongly, and 

 throwing a brilliant light upon the neighbouring clouds. It 

 lasted about five minutes with perfect steadiness, and then 

 gradually disappeared. 



I ought to mention, that, during the above-described phe- 

 nomena, violent thunder-storms were taking place in different 

 parts of this county and in Cheshire, but without any apparent 

 connexion with them. 



I have the honour to remain, Gentlemen, 



Yours very respectfully, 



Acton Square, Salford, Manchester, James P. JoULE. 



July 19, 1850. 



