Electro-Meteorological Observations. 307 



of the atmosphere, and approaches nearest to it when the dew point 

 continues very low, and vice versa. 



It is well known that when a body charged with positive electri- 

 city, approximates another negatively electrified, having a bad con- 

 ductor between them, the positive electricity has a tendency to whiz 

 off.* These facts being admitted it follows that when one body, (as 

 the air,) being charged with positive electricity, approaches another, 

 (as the earth,) negatively electrified, the positive electricity will whiz 

 off and produce in the dark, those beautiful diffused and continued 

 flashes known as the aurora borealis.f 



The magnetic needle is deranged in proportion to the brightness 

 of the aurora, which is another proof that the proximity of the posi- 

 tive electricity to the surface of the earth is the cause of the aurora 

 borealis and australis. 



If the higher strata of the air are at all times charged with the 

 electric fluid in an opposite state to that of the earth there must ex- 

 ist a great excitement between them ; for if a small glass tube be 

 rubbed it will cause pieces of paper to stand on end. Now if so 

 small a quantity of electric fluid will produce so great an excitement, 

 what must be the effect of the immense body of electrified air on 

 the living objects on the surface of the earth ? May not animal and 

 vegetable life depend upon that excitement, and if it does, would 

 not an increase or diminution of that excitement as the fluid ap- 

 proached or receded from the surface of the earth, depress, or stim- 

 ulate the vital action and cause disease ? May not epidemics be 

 produced in this way ? The traveling of epidemics could be ac- 

 counted for on this principle, for when one portion of the air hap- 

 pens to contain more or less of the fluid than the rest, it would be dis- 

 tributed to, or subtracted from the other portions until all were equally 

 electrified, and thus carry the epidemic from one country to another. 



Experiments of this nature would show whether at the time of an 

 epidemic there was a difference in the height of the lower surface 

 of the positive fluid, and what height was necessary to produce it. 

 They would also show if comets, volcanic eruptions, &.c. affect the 

 electric state of the air. 



* The electric brush, for example, produced from a point suspended above a 

 conducting surface, is an aurora on a small scale; the rays of light are only seen 

 above, where the fluid is given off. 



t " The aurora may arise from discharges from one ocean o^ electricity to the 

 other, which, not being concentrated by its attraction for intervening clouds within 

 air sufhciently dense to act as an electric, assumes the diffuse form which charac- 

 terizes that phenomenon." — Prof. Hare's paper on the Water Spout, Aurora, if-c. 



