ion of a Solar Electric Potential. 163 
brought about by the powerful ascending and descending 
currents in the sun's atmosphere which must arise from the 
combustion of the elements cooled by expansion and the cool- 
ing of the burnt outermost layers of the photosphere by radia- 
tion, will continually be equalized again by friction against 
each other of the parts of the sun's atmosphere rotating with 
different velocities. About the height of this atmosphere 
rotating equally with the sun's body nothing is yet known. 
According to Bitter's calculations*, indeed, the density of 
the solar atmosphere diminishes very quickly (following the 
sudden alteration of the adiabatic curve) in the region of the 
photosphere, in which the supply of heat from combustion con- 
siderably retards the diminution of temperature correspond- 
ing to the progressive rarefaction ; but we do not yet know 
the limit of rarefaction up to which Mariotte and Gray-Lussac's 
law holds good. If, however, the atmosphere reaches the 
limit at which the force of attraction and the centrifugal force 
counterbalance each other, every material molecule passing 
beyond this must henceforth revolve round the sun like a 
planet. If new particles of the mass were constantly arriving 
at and entering this limit, a progressive condensation of 
matter would of necessity take place and a ring be formed 
here, which would rotate round the sun in accordance with 
Kepler's laws. Presupposing, however, the continuity of the 
sun's atmosphere, this ring-formation cannot occur, since the 
mutual friction of the strata of gas continues even beyond the 
surface of equilibrium, and consequently those which are al- 
ready in planetary motion are subjected to an acceleration. 
The result must be that with the increase of velocity the dis- 
tance of each of these microplanets from the sun is perpe- 
tually increasing; consequently the constant outflow from the 
solar atmosphere into cosmical space, assumed by my brother, 
must actually take place. And it can only take place in the 
zone of the sun's equator, since here at equal distance from 
the centre the centrifugal force is the greatest. It must also 
be admitted that the density of this atmosphere, everywhere 
rotating in accordance with Kepler's laws, in the plane of the 
sun's equator remains constant up to great distances from the 
, sun, since the solar gravitation is throughout equilibrated by 
the velocity of revolution. In the directions perpendicular to 
that plane, on the contrary, the density must decrease, since 
the solar attraction diminishes as the distance from the plane 
of the sun's equator increases. 
It follows from this consideration that a material current 
emanating from the sun coincident with the phenomenon of the 
* Wied. Ann. v. p. 405, 1878. 
02 
