512 Mr. D. Vaughan on Phenomena which may be traced 
The definite information which Arago was enabled to furnish 
respecting the sun by means of his polariscope, has recently 
received an important accession from the labours of Bunsen and 
Kirchhoff. A comparison of the spectrum of the sun with that 
of various metallic vapours in a state of incandescence, enabled 
these chemists to show that potassium, sodium, calcium, and 
other elements widely diffused on our globe, enter into the com- 
position of the solar atmosphere. Their observations proved, 
however, that these substances, while abundant in the sun’s en- 
velope, instead of being concerned in producing his light, only 
exerted a negative influence—absorbing certain rays, and causing 
dark lines to replace the bright ones peculiar to their luminous 
vapours. It is therefore evident that the light from the vapours 
of the elements alluded to must be overpowered by the rays 
emanating from some other source. Professor Kirchhoff has 
embraced the opinion that the solid globe of the sun must have 
a far higher temperature and a greater illuminating power than 
his atmosphere; but the observations with Arago’s polariscope 
have afforded positive evidence that solar light does not emanate 
from an incandescent solid or liquid body. It appears more 
philosophical to conclude that the hght of our great luminary 
originates, not from the vapours discoverable in its atmosphere, 
but from a more subtle ethereal medium combined with them, 
and possessed of far greater illuminating power. 
The periodical changes recently discovered in the sun’s spots 
seem to furnish a fatal objection to the idea that the self-luminous 
condition results from the high temperature of his solid nucleus, 
or from the heat developed by its compression. It can scarcely be 
doubted that the periodicity of the spots is dependent on the 
movements of the planets; and the position of Jupiter seem to 
exert the greatest influence on their cecurrence; as recent ob- 
servations show, the period of his revolution agrees very closely 
with the interval between the times at which the spots are most 
numerous. Although it may be premature to express a decided 
opinion on so obscure a subject, there seem to be legitimate 
motives to justify an examination of the more obvious ways in 
which it would be possible for a planet to affect the luminous 
condition of the solar disk. If, as Helmholtz contends, the 
ocean of heat and light be maintained by the compression of the 
sun, the planets can only exert their influence on his spots by 
diminishing the weight and pressure of his materials, in the same 
manner in which the moon acts to raise tides on our oceans. 
But the alteration in the weight of terrestrial matter from lunar 
attraction, though extremely small, is about 80,000 times as great 
as that which the component parts of the sun experience from the 
attractive force of Jupiter. ‘This planet holds the highest place 
