THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



SEPTEMBER 1849. 



XXII. On the Production of Lightning hy 'Rain. 

 By William Radcliff Birt*. 



f\^ the 26th of July, IS-tQ, a severe thunder-stoiin,accompa- 

 ^^ nied by the destruction of property and the loss of human 

 life, passed over the metropolis. About 1^' 30™ p.m. the clouds 

 towards the north-east presented a very dark and threatening 

 aspect; they assumed an inky colour, and the velocity of their 

 motion was very slow ; in fact the appearance noticed was 

 strikingly of that character which the writer has frequently 

 observed to precede a thunder-storm. On this occasion his 

 attention was more particularly directed to the connexion 

 between the electric discharge and the sudden gush of rain 

 that more or less accompanies it, with a view to illustrate the 

 question occurring in the Report of the Committee of Physics 

 approved by the President and Council of the Royal Society, 

 p. 46, " Is this rain a cause or consequence of the electric dis- 

 charge ?" t On the previous day, the 25th, about 3^ 50°* p.m., 

 during a thunder-storm a sudden gush of heavy rain occurred, 



* Communicatecl by the Author. 



\ The paragraph runs thus : " There is one point to which we wish that 

 some attention might be paid, — it is the sudden gush of rain which is almost 

 sure to succeed a violent detonation immediately overhead. Is this rain a 

 cause or consequence of the electric discharge? Opinion would seem to lean 

 to the latter side, or rather, we are not aware that the former has been main- 

 tained or even suggested. Yet it is very defensible. In the sudden agglo- 

 meration of many minute and feebly electrified globules into one rain-drop, 

 the quantity of electricity is increased in a greater proportion than the sur- 

 face over which (according to the laws of electric distribution) it is spread. 

 Its tension therefore is increased,and may attain the point when it is capable 

 of separating from the drop to seek the surface of the cloud, or ofthe newly- 

 formed descending body of rain, which under such circumstances, and with 

 respect to electricity of such a tension, may be regarded as a conducting 

 medium. Arrived at this surface, the tension for the same reason becomes 

 enormous, and a flash escapes." 



Phil. Mag. S. 3. Vol. 35. No. 235. Sept. 1849. M 



