1904-5.] On Prof. Seeligers. Theory of Temporary Stars. 521 
unlimited. I have mentioned already that the surface tempera- 
ture of a Nova may exceed many times that of the solar photo- 
sphere.* Hence there is no reason to contradict the assertion that 
the atmosphere of a new star, after the catastrophe, may assume 
dimensions surpassing considerably even those presented in the 
white stars. Indeed, this atmosphere may even extend infinitely, 
for it is well known that when the temperature of the surface 
exceeds a certain critical value, the height of the atmosphere 
above the surface must become infinite, i.e. gravitation then 
proves insufficient to counteract the continuous dissipation of the 
gases into space. As is shown in the paper referred to, this state 
of matters may happen already at a comparatively low tempera- 
ture, exceeding not many times that of stars of the Sirian class 
(i.e., 118). Now, in this peculiar case of infinite expansion, the 
initial velocities of the gaseous molecules at the surface must have 
been greater than the so-called critical velocity of the star (i.e. 
610 km. per second if the sun’s mass and dimensions be assumed). 
* Some estimate of the amount of heat developed by the impact may be 
gained from the following consideration. Suppose the materials of a cosmic 
cloud to fall from infinity upon our sun. The velocity Y with which the 
cloud particles arrive at the sun’s surface is hyperbolic, and therefore 
greater than 600 km. per second. Now we know that 1 kgr. matter moving 
with a velocity of Y metres per second, if completely stopped, develops a 
quantity of heat which equals — — • v 1 calories. If, then, a quantity of 
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cosmic matter weighing 1 kgr. at the surface of the earth would impinge 
upon the sun with parabolic velocity (about 600,000 metres per second), ca. 
45 millions of calories would be developed by the collision. Suppose that 
during every second 1 kgr. matter impinges upon the area of 1 square metre, 
then the heat developed would be about 2400 times the amount of heat 
actually radiated by our sun during the same time. Now it is easy to see 
that this kgr. of matter is distributed within a parallelopipedon whose basis 
is 1 square metre and whose height is 600 km., because when the first 
particle of the kilogram arrives at the surface, the last particle which 
impinges exactly one second later will be, roughly speaking, at a distance of 
600,000 metres from the surface. But the density of such a cloud is only 
about 1 : 800,000 of the density of air at ordinary temperature and pressure. 
Hence we conclude that an all-round impact of cosmic matter whose density 
is only the 1 : 2,000,000,000th part of that of our atmosphere would still 
produce an amount of heat equivalent to the energy radiated into space 
during the same time by our sun under normal circumstances. This rough 
calculation appears to justify the remark in the text, that the amount of 
heat supplied by the collision may indeed be assumed to be practically 
unlimited. 
