GREAT FIRES AND RAIN-STORMS. 211 



the northwest. "We know by various indications that the air is highly 

 electrified. The wind blows too freshly to place our water-dropper 

 out-of-doors ; accordingly, it is placed upon a table in the laboratory, 

 and we notice the indication of the instrument. The air is indeed 

 highly charged the spot of light is thrown to a greater distance upon 

 the scale than we have often noticed. Let us record the reading ; it is 

 as much as the positive pole of twelve Daniell cells gives. Now, 

 lighting our Bunsen gas-burner, and placing it near our water-dropper, 

 let us observe the spot of light ; it does not change its position mate- 

 rially at first. 



Now, after the lapse of a few minutes, it falls to a lower position 

 upon the scale, now it goes down to zero. Now it mounts again, but 

 in a contrary direction to its first indication, showing a slight nega- 

 tive charge in the air, which before was strongly charged positively. 

 Can this be due to the presence of the flame ? And, if it is due to the 

 flame, are not great fires capable of influencing the electrical state of 

 the atmosphere, to a greater or less extent ? Such are the questions 

 which force themselves upon us. We must, in the first place, examine 

 our flame. Soldering a platinum wire to the copper connecting wire, 

 and dispensing with the water-dropper, we examine the outer and 

 inner cone of the flame. At all points in the luminous portion of the 

 flame an indication of negative electricity is obtained ; at all points in 

 the immediate neighborhood of the flame, but exterior to it, there are 

 signs of a positive charge in the heated air. The inner cone of partly- 

 consumed gas is neutral, or slightly negative. 



The flame, therefore, is negative, and it tends by its presence to 

 reduce the positive charge of electricity which generally characterizes 

 the air of fine weather to zero, or to change it to a feebly negative- 

 charge. We learn from various writers upon meteorology that the 

 normal electricity of the atmosphere is positive. Herschel in his 

 work on Meteorology says, p. 125 : " Out of 10,500 observations made 

 at the Kew Observatory in 1845-47, 10,176 showed positive, and only 

 364 negative electricity the latter being almost always accompanied 

 with heavy rain." Sir William Thomson, in the proceedings of the 

 Literary and Philosophical Society of Manchester, March, 1862, relates 

 some experiments which tend to show that clearing-up weather is 

 preceded, and in many cases foretold, by a change in the atmosphere 

 from a negative to a positive charge of electricity. 



We can, therefore, conclude with some probability of truth that 

 great fires, by changing the electrical state of the atmosphere, have an 

 influence upon the production of rain. The state of our knowledge, 

 however, in regard to the part that electricity plays in atmospheric 

 changes, is very meagre. The question of the truth of the popular 

 belief that great fires are followed by rain still remains unanswered ; 

 and we can only hope that we have thrown a little more light upon it 

 by our research. 



