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 i oleae 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.+ 
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 cde for — produced from a point.suspended above a 
conducting surface, is an urora on a small scale; the rays of light are only seen 
Soe where the flui ve of. 
“The aurora may e ocr from discharges from one ocean of electricity to the 
whie jts attraction for Within 
air sufficiently dense to act as an electric, assumes the diffuse Leica hicks ued 
terizes that phenomenon.” —Prof. Hare’s paper on the Water Spout, Aurora, ¢-c, 
‘ 
