THE SOURCE OF HEAT IN THE SUN. 
153 
the circumference of its denser mass^ in which floats those 
illuminated vapours which are too attenuated to be seen except 
when the Sun^s light is obscured. Below this is the photo- 
sphere — an ocean of light whose waves assume those willow- 
leaf forms which are remarkable in shape and size. Then^ 
whenever by disturbances^ which are clearly generated below 
this luminous sphere^ the motion necessary to the formation 
of a dark spot is produced_, we look into a region of penumbral 
clouds, and through these into a yet darker space. That the 
disturbances which have been observed to take place on the 
Sun^s surface are evidences of physical energies promulgated 
on the most extensive scale, is proved by the fact that the 
formation of dark spots influences the magnetism of this earth. 
We know that an order of periodicity prevails in the inten- 
sity of the force of terrestrial magnetism, and we are convinced 
now that this is determined by the formation of solar spots. 
On one occasion two observers, far apart,* were observing a 
dark spot on the Suu, when there was a sudden outburst of 
light, which was due to the rushing of the willow-leaved forms, 
at the rate of 7,000 miles in a minute, to bridge over the vast 
opening in the photosphere. It is necessary to understand 
this, to state, that although at all ordinary times those willow- 
leaves lie at random, they arrange themselves symmetrically 
around a dark spot, and front inwards, like sedgy grasses 
streaming out into the waters of a pond. The sudden outburst 
of light which has been mentioned was due to the floating out 
of these forms, as in bridges, to cover in the opening {see 
Plate YI.) in this hght developing ocean. When this oc- 
curred the Earth had her indications of it. Every magnetic 
bar in our observatories trembled, Aurora quivered in the 
skies, and our telegraphic wires were perplexed with the 
additional quantity of electricity which they had to carry. 
Such are the manifestations of solar energy — how is this 
developed ? and being constantly developed, how is it main- 
tained ? Spectrum analysis has taught us that the dark lines 
in the solar spectrum give us indications of the combustion 
of matter in the Sun. {See Popular Science Review, Yol. I. 
p. 212.) The investigations of Kirchoff, Bunsen, Angstrom, 
and others, prove that the vapours of nickel, cobalt, iron, 
manganese, copper, zinc, barium, sodium, magnesium, chro- 
mium, calcium, aluminium, strontium, are present in the sun^s 
gaseous envelope, and that hydrogen is also there. These 
metals must therefore be burning, in the mass of the Sun, to 
give that vapour which is detected in the SuAs atmosphere. 
If these results are received as truths, it may appear that the 
* Mr. Carringrton and Mr. Hodgson. 
