FEBRUARY 1, 1901.] 
taken with eight or ten telescopes, mostly 
in Europe. 
Assistant-astronomer C. D. Perrine, as- 
sisted by Mr. Palmer, is employing the 
Crossley Reflector every clear night to ob- 
tain photographs of Eros and its surround- 
ing stars, to furnish the planet’s accurate 
position in the evening, in the morning, and 
onthe meridian. The measurement of these 
plates will be a heavy task. Fortunately, 
Professor Rees, Director of the Columbia 
University Observatory, has volunteered to 
measure them. Columbia University is 
the only institution in this country which 
has had experience in measuring such 
plates, though many foreign observatories 
have long been doing similar work. 
The planet Eros is now of about the 9.3 
magnitude. It is easily visible in a three- 
inch telescope. 
W. W. CAMPBELL, 
Director of the Lick Observatory. 
ON THE NATURE OF THE SOLAR CORONA, 
WITH SOME SUGGESTIONS FOR WORK 
AT THE NEXT TOTAL ECLIPSE. 
In an article on the corona, published in 
the November number of the Astrophysical 
Journal, I suggested a method by which the 
existence of the Fraunhofer lines in the 
spectrum of the corona might be detected. 
The method was based on the supposition 
that the light emitted by the particles in 
virtue of their incandescence, s0 overpowers 
the reflected sunlight that the lines are in- 
visible. That the coronal light is strongly 
polarized is well known, and there is 
scarcely any doubt but that the polarized 
light is reflected sunlight. If now a Nicol 
prism be placed before the slit of the spec- 
troscope in such a position as to transmit 
the polarized radiations, these will be al- 
lowed to pass with almost undiminished 
intensity, while the emitted or unpolarized 
light will be reduced in intensity by one- 
half. The great change in the ratio result- 
SCIENCE. 
Wes 
ing might easily be sufficient to bring out 
the dark lines distinctly. I feel firmly con- 
vinced that this experiment should be tried 
at the Sumatra eclipse of next May, for I 
have successfully accomplished it in the 
laboratory with an artificial corona. It was 
found that a gas flame in a strong beam of 
sunlight shone with a pure bluish-white 
light, due to the reflection or rather scat- 
tering of the sunlight by the minute carbon 
particles.* The flame thus illuminated 
showed the Fraunhofer lines distinctly, but 
by reducing the intensity of the sunlight a 
point was reached at which they disap- 
peared, and the spectrum appeared con- 
tinuous. The light scattered by the flame 
was found to be completely plane-polarized 
in certain directions, giving us just the 
required conditions, namely particles emit- 
ting a continuous spectrum, and scattering 
a polarized solar spectrum. In front of the 
slit of the spectroscope a Nicol was ar- 
ranged in such a manner that it could be 
drawn into and out of position by a cord. 
The Fraunhofer lines could be made to. 
appear by sliding the Nicol in front of the 
slit, and disappear by drawing it away. 
While it does not by any means follow that 
the use of a Nicol on the actual corona 
will bring out the lines, the experiment 
seems to be well worth trying, as it would 
furnish further information regarding the 
relative intensity of the emitted and re- 
flected light. Another interesting point is 
that the minute particles in the flame do 
not scatter the longer waves, the flame re- 
flecting practically no red or orange light. 
Thus the Fraunhofer Jines can only be 
traced up to about the D lines. By gradu- 
ally reducing the intensity of the sunlight 
they disappear first in the yellow, then in 
the green, blue, and violet in succession. 
* A photograph of the flame with a spot illumi- 
nated by powerful convergent beams of sunlight fur- 
nishes a beautiful proof of the existence of solid 
particles in the flame. 
