PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 1 MARCH 15. 1915 Number 3 
AN ATTEMPT TO MEASURE THE FREE ELECTRICITY IN THE 
SUN'S ATMOSPHERE 
By George E. Hale and Harold D. Babcock 
MOUNT WILSON SOLAR OBSERVATORY. CARNEGIE INSTITUTION OF WASHINGTON 
Presented to the Academy, January 16. 1915 
We have the strongest of reasons to infer the existence of free elec- 
tricity in the sun. At high temperatures in the laboratory carbon and 
other elements emit great numbers of negatively charged particles, 
while friction, collision and exposure to ultra-violet light may be men- 
tioned among various other agencies capable of producing free elec- 
trons under solar conditions. On the other hand, the presence of in- 
tense magnetic fields in sim-spots points to a marked preponderance 
of negative electrons whirling in the spot vortex. Thus, without ad- 
ducing further evidence, we find that both laboratory results and solar 
phenomena indicate the presence of free electricity in various parts of 
the solar atmosphere.^ 
The greater mobility of negative electrons and the influence of light 
pressure must cooperate to transfer negative electricity toward the 
upper levels of the atmosphere, thus leaving the body of the sun with 
a positive charge. However, hot vapors and gases are such good con- 
ductors that any considerable potential difference would tend to be 
compensated by a flow of current. In the presence of complex and un- 
certain conditions, such as the possible influence of radio-active sub- 
stances, definite and unimpeachable knowledge of solar electric phe- 
nomena must be based upon a direct method of observation, which has 
recently become available through Stark's capital discovery of the 
effect of an electric field on radiation. If adequately applied, this 
method may ultimately furnish as reliable information of solar elec- 
tricity as the Zeeman effect has already afforded of solar magnetism. 
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