1885.] 
The Heat of the Sun. 137 
disc of matter rapidly leaving him, and at the Poles matter 
approaching him. Tn this way, Dr. Siemens says, enormous 
quantities of “ hydrogen, hydrocarbons, and oxygen are 
supposed to be drawn towards the polar surfaces of the 
Sun. “ During their gradual approach they will pass from 
their condition of extreme attenuation and extreme cold to 
that of compression, accompanied with rise of temperature, 
until on approaching the photosphere they burst into flame’ 
giving rise to a great development of heat, and a temper- 
atuie commensurate with their point of dissociation at the 
solar density. The result of their combustion will be 
aqueous vapour and carbonic anhydride or oxide, according 
to the sufficiency or insufficiency of oxygen present.” These 
products of combustion will come under the influence of 
centrifugal force, and move towards the Equator, where 
they will be projected into space. As they recede from the 
Sun they gradually lose their heat, and become more and 
more rarefied, until they obtain the extreme state of rare- 
faction which they possess in inter-planetary space. Here 
it is supposed the inverse adtion to that which occurs in the 
Sun takes place. The now highly rarefied aqueous vapour 
and carbonic anhydride absorb some of the radiations 
which the Sun is constantly pouring out, and it is supposed 
that at the extremely low pressure to which they are sub- 
jected they are dissociated, oxygen, hydrogen, and hydro- 
carbons being produced. These are in turn again drawn in 
to the polar surfaces by the fan-like adtion produced by the 
solar rotation. Thus we see that a continuous circulation 
of matter occurs, the same element alternately forming a 
portion of the coldest portion of inter-planetary space, and 
the hottest portion of the central luminary. 
Such in outline are the chief points of this latest theory 
of solar adbion. There are some other secondary points 
which are rendered necessary in consequence of the known 
constitution of the Sun. For example, we know that the 
solar atmosphere contains large quantities of the vapour of 
certain metallic bodies. These are supposed to constitute 
an inner atmospheric shell which is not affedted, in conse- 
quence of their density, by the centrifugal force caused by 
rotation. This force, in fadb, only affedts the lighter mate- 
rials, chiefly hydrogen constituting the circulating atmo- 
sphere. At the surface of contact between the two, 
however, intermixture induced by fridbion may sometimes 
occur, “ giving rise to those vortices and explosive effedbs 
which are revealed to us by the telescope. . . . Some of the 
denser vapours would probably get intermixed and carried 
vol. vn. (third series). m 
