791 



till 2 h in the afternoon, in trying" it with the 

 electrometer of Volta, on a terrace thirty feet 

 high, and entirely open, becomes suddenly so 

 strong that the divergence of the balls rises to 

 eight lines, and it is soon no longer necessary 

 to arm the instrument with a wick. The elec- 

 tricity often passes from positive to negative, 

 without thunder being heard. In a great num- 

 ber of storms the electric charge of the. air ap- 

 peated to me to be negative twenty minutes 

 before the strongest explosions, although I 

 made my experiments far from any trees, in the 

 middle of the Salado, in a vast plain. The rain 

 that falls during the storm, is sometimes of the 

 temperature of 17.8° ; and I then found it a 

 degree colder than the air, at the moment of 

 the shower. Having made many experiments 

 in the open country, in temperate climates, at 

 Salzbourg, Bayreuth, Vienna, Marseilles, and 

 Corogne, I can affirm that the electric charge, 

 which becomes sensible within the tropics, 

 during the storm, in the low regions of the air, 

 is of surprising intensity. After three quarters 

 of an hour of storm, lightening, and rain, I saw 

 in the electrometer of Volta, without the con- 

 ductor being armed with a wick, a separation 

 of the balls of ten lines. Often, at the instant 

 of the thunder, the electricity does not change 

 from + into — , or from — into + ; sometimes 

 these passages are not accompanied with any 



