24 



Proceedings of the Royal Irish A cademy. 



the night of May 14th. A slight shower had fallen earlier in the evening 

 but the first peal of thunder was heard about 9.50 p m.' From 10.30 p.m. till 

 1 a.m. the thunder and lightning were alnipst incessant. Ilain did not begin 

 to fall till about 10.20, so that it was possible to get observations throughout 

 the entii'c thunderstorm. At first the rain was very light, hut became 

 exceedingly heavy from 10.40 to 11 o'clock. It continued to be fairly heavy, 

 with one or two lulls throughout the storm. The charge at first was negative 

 and high, 3-6 E.S.U. per c.c. After about ten minutes it became positive, 

 but the positive cliarge per c.c. was not so large, generally 1-2 E.S.U. 

 The charge changed in sign several times, and during these changes the 

 values were sometimes quite low. A negative charge of 5 E.S.U. per c.c. 

 was got again at 12.45, and from 12.50 till near the end a positive charge of 

 2-5 E S.U. per c.c. was recorded. 



Sign 



Number of observations, allowing charge per c.c. 



of charge. 



1 E. S. U. 



1-3 E. S. U. 



3-5 E. S. C. 



Total No. of 

 obser\'aIions. 



+ 



17 

 U 



28 

 12 



4 



12 



49 



.38 



Average positive charge per c.c. = 1'62 E.S.U. 

 Avei-age negative charge per c.c = 203 E.S.U. 



It is perhap-s worthy of note tliat in this stonn the highest charges, both 

 positive and negative, occurred with the heaviest rain. The rate of fall 

 between 10.40 and 11 o'clock was over 5 mms. per hour. 



The other thunderstonii occurred after 10 p.m. on June 4. Only two 

 short, heavy showers fell. The first of these was missed. The second, lasting 

 about ten minutes, gave seven readings, of which five were negative and two 

 (not consecutive) positive. 



Average positive charge per c.c. = '45 E.S.U. 

 Average negative charge per c.c. = 43 E.S.U. 



Highest negative charge per c.c. in shower = 108 E.S.U. 

 Highest positive charge per c.c. in sliower = •73 E.S.I^. 



In both these storms the rain was sometimes positively charged, some- 

 times negatively ; and the charge per c.c. was in each case larger than is 

 usually obtained with non-thunderstorm rain. 



> Ball lightning observed. M'Clelland and Gilmour: Nature. 12th June, 1910. 



