SCIENTIFIC SUMMARY. 
85 
the behaviour of sun-spots, a suggestion of the illustrious Galileo, which he 
appears not to have published from want of evidence, has been brought to 
light by the Rev. William Selwyn. This suggestion advocates a method of 
research allied to that in which the Kew astronomers are now engaged. 
Spectroscopic Observations of the Sun is the title of a paper recently 
presented to the Royal Society by Mr. J. Norman Lockyer. The author re- 
marks that the two most recent theories dealing with the physical con- 
stitution of the sun are due to M. Faye and to Messrs. De la Rue, Balfour 
Stewart, and Loewy. The chief point of difference in these two theories 
is the explanation given by each of the phenomena of sun-spots. Thus, 
according to M. Faye, the interior of the sun is a nebulous gaseous mass 
of feeble radiating-power, at a temperature of dissociation ; the photo- 
sphere is, on the other hand, of a high radiating-power, and at a temperature 
sufficiently low to permit of chemical action. In a sun-spot we see the 
interior nebulous mass through an opening in the photosphere, caused by an 
upward current, and the sun-spot is black, by reason of the feeble radiating- 
power of the nebulous mass. In the theory held by Messrs. De la Rue, 
Stewart, and Loewy, the appearances connected with sun-spots are referred 
to the effects, cooling and absorptive, of an inrush, or descending current, of 
the sun’s atmosphere, who is known to be colder than the photosphere. 
In June 1865 the author communicated to the Royal Astronomical Society 
some observations which had led him independently to the latter conclu- 
sion. The observations indicated that, instead of a spot being caused by 
an upward current, it is caused by a downward one, and that the results, 
or, at all events, the concomitants, of the downward current are a dimming 
and possible vaporisation of the cloud-masses carried down. 
On March 4 of the present year a spectroscopic observation of sun-spots 
was commenced, with a view of endeavouring to test the two rival theories, 
and especially of following up the observations before alluded to. 
On turning the telescope and spectrum-apparatus, driven by clockwork, 
on to the sun at the date mentioned, the solar spectrum was observed in the 
field of view of the spectroscope with its central portion (corresponding to 
the diameter of the umbra falling on the slit) greatly enfeebled in brilliancy. 
All the absorption-bands, however, visible in the spectrum of the photo- 
sphere, above and below, were visible in the spectrum of the spot ; they, 
moreover, appeared thicker where they crossed the spot-spectrum. 
Mr. Lockyer was unable to detect the slightest indication of any bright 
bands. 
Should these observations be confirmed by observations of a larger spot 
free from lt cloudy stratum,” it will follow, not only that the phenomena 
presented by a sun-spot are not due to radiation from such a source as that 
imagined by M. Faye, but that we have in this absorption-hypothesis a 
complete or partial solution of the problem which has withstood so many 
attacks. 
The paper concludes as follows : u Seeing that spectrum-analysis has 
already been applied to the stars with such success, it is not too much to 
think that an attentive and detailed spectroscopic examination of the sun’s 
surface may bring us much knowledge bearing on the physical constitution 
of that luminary. For instance, if the theory of absorption be true, we may 
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