1904-5.] On Prof. Seeliger’s Theory of Temporary Stars. 517 
cloud particles, in obedience to gravitational laws, describe hyper- 
bolic orbits round the star’s centre as focus, in exactly the same 
manner as do those meteoric swarms of our own system which 
have been launched upon us from the remote recesses of space. 
The idea occasionally met with in papers on this subject, that the 
star penetrates into the cloud as a bullet pierces the air, is 
quite erroneous. Its fallacy is so obvious that I need not dwell 
upon it. 
The hyperbolic paths described by the attracted particles are of 
course extremely different in shape and position, forming a chaos 
of motions which to unravel seems at first sight a hopeless task. 
But, fortunately, at least one definite conclusion may be drawn 
which is of vital importance for our problem. We know that the 
character of the conic section described by a body round a centre 
of attraction is perfectly defined by its velocity Y at any point of 
the orbit. The body describes 
an ellipse, 
a parabola, 
if Y2< 2 _^ 
r 
if V2 = 
r 
a hyperbola, if V 2 > 
r 
/x = ft 2 (M + m) 
where r is the radius vector at that point (expressed in units of 
the mean distance 0 - J ), k the Gaussian constant, and M, m 
the masses of the attracting and attracted body in units of the 
solar mass. Now, in our case a collision between the star and a 
meteoric particle must occur in all instances where the perihelion 
distances are less than the radius of the star. Such particles will 
impinge upon the surface. But impact means loss of energy of 
motion (molar energy), which is converted into kinetic (molecular) 
energy, i.e. heat. Hence Y, the orbital velocity, must be smaller 
after the impact than it had been before. In other words, the 
impact-friction on and near the star’s surface, by converting a more 
or less considerable portion of energy of motion into energy of heat, 
acts as a resisting medium, with the effect that in many cases Y 
becomes less than i.e. that the hyperbolae are transformed 
into ellipses. 
