Conservation of Solar Energy. 65 
he reintroduces the effect of projection into space by centri- 
fugal force, and makes the remarkable statement that "if 
owing to centrifugal force H is projected x miles into space, 
then sodium vapour, which is 23 times as heavy, will be pro- 
jected ^ miles." Surely a pound of one substance is as 
good as another as regards vis inertia? and gravitation; and it 
seems an unfair proceeding on the part of the latter force to 
recall the one sooner than the other simply because it is the 
denser of the two. Considering, however, that the force of 
gravity is 46,800 times greater than centrifugal force upon the 
solar equator, no substance could be projected outward a single 
inch by centrifugal force, although that force is capable of de- 
termining the outflow of a gaseous column, balanced by an 
inflowing polar current of nearly the same density, thus giving 
rise to what I termed the solar " fan action." 
Mr. Cook remarks very properly, that my hypothesis, if 
applicable to the Sun, must be equally applicable to Sirius 
with its bluish-white and to Arcturus with its reddish light; 
and he says "it is difficult to see how these differences are 
to be accounted for "on the principle of combustion, "the 
same atmosphere supplying them all." But surely the tem- 
perature of terrestrial coal-furnaces is not always the same, 
depending, as they do, upon the intensity of the draught and 
the density of the fuel employed. In the case of the photo- 
sphere the richness of the gaseous fuel is determined by its 
density (that is, by the magnitude of the solar body), and the 
intensity of the combustion by the draught (that is, by its 
tangential velocity), both of which may vary between wide 
limits ; and the latterjjmay be slowly diminishing, thus giving 
force to Dr. Huggins's suggestion of the effect of age. The 
brilliancy of a fixed star must depend moreover upon our rela- 
tive position towards it, being partially obscured perhaps, if 
seen equatorially, by planetary matter. 
In conclusion, allow me to refer Mr. Cook to the last issue 
of the Proceedings of the Berlin Academy. In it one of its 
members (my brother, Dr. Werner Siemens) gives a full 
investigation of the nature and causes of the electric potential 
supposed to exist between the Sun and our planet. After 
some hesitation, my brother has arrived at the conclusion that 
this electrical connexion cannot be satisfactorily explained 
except by adopting my hypothesis of a material equatorial 
outflow, sweeping out from the Sun past our Earth, and car- 
rying with it particles of dust. When writing this article, 
my brother appears to have overlooked the most interesting- 
observations that have been made for some years at the Green- 
Phil. Mag. S. 5. Vol. 16. No. 97. July 1883. F 
