386 Electrical Excitation. 



JlET, XXYIIL — On a New Source of Electrical Excitation; by 



Mrs. Elisha Foote, 



(Eead before the American Association at Montreal, Aug. ISth, 1857.) 



I HAVE ascertained that the compression or the expansion of 

 atmospheric air produces an electrical excitation. So far as I 

 am aware this has not been before observed, and it seems to me 

 to have an important bearing in the explanation of several at- 

 mospheric and electrical phenomena. 



The apparatus used was an ordinary air-pump of rather feeble 

 power and adapted either to compress or exhaust the air. Its 

 receiver was a glass tube about twenty-two inches in height and 

 three in diameter, with its ends closed by brass caps cemented to 

 it At the bottom was a stop-cock and a screw by which it w^as 

 attached to the air pump. To the top were soldered tw^o copper 

 wires, one hanging down within the tube, terminating in one or 

 more points and extending to within about six inches of the 

 bottom, the other extending from the upper side of the cap to 

 an ordinary electrical condenser. 



In experimenting after compressing or exhausting the air 

 within the receiver, the wire reaching to the condenser was dis- 

 connected from it. The upper plate was lifted from its place by 

 its glass handle and its electrical condition tested by a gold leaf 

 electrometer. I have found it convenient first to compress the 

 air and close the stop-cock, when the condenser would be found 

 to be charged wath positive electricity. Then after dischargmg 

 all traces of it both from the condenser and the wire leading to 

 itj the air was allowed to escape, and the condenser would be- 

 come recharged to an equal extent. 



My experiments with this apparatus have extended over about 

 eight months, and I have found the action to bear a strong anal- 

 ogy to that of the electrical machine. In damp or warm weather 

 little or no effect -would be produced, whilst at other times, par- 

 ticularly in clear cold weather, the action would be so strong as 

 to diverge the leaves of the electrometer to their utmost extent. 

 In warm weather when no action would be produced, I have at- 

 tained the result by cooling the air artificially. A sudden ex- 

 pansion or contraction always increases the eflfect. 



The results with oxygen gas were similar, but I was not suc- 

 cessful with either hvarogen or carbonic acid gases. 



It is believed that" the results which have been obtained on a 

 «mall scale in my experiments may be traced in the great opera- 

 tions of nature. The fluctuations of our atmosphere produce 

 compressions and expansions sufficient to cause great electrical 

 disturbances. Particularly should this be observed in the dry 

 cold regions of our atmosphere above the effects of moisture ana 



