66 
radiation as our sun, ie. 4,2.10°* ergs per second. The energy 
absorbed by the nebula per second is 5,1 .10* ergs. The pressure 
of radiation can be calculated in this case with the well-known 
formula: 
S 
dD = Em) . . e . . . . . . (1) 
C 
in which S == quantity per second of received radiation in ergs, 
5 den 5 7 é 
e=3.10" ~~, D = pressure of radiation in dynes. 
sec. 
This yields in our case: 
D = 1,7%, 10! dynes, 
Putting the mass of the nebula, like that of the star, about equal 
to that of the sun, ie. 2.10 gr, we find for the maximum 
acceleration through pressure of radiation: 
cm 
e= 0.3% L0j ; 
Sec 
for that of the attraction: 
‘nN 
a= 14 10-1 
sec 
Accordingly by the side of the attraction the pressure of radiation, 
even when calculated on exceedingly favourable suppositions, is 
almost negligible. As the same ratio must be valid with regard to 
the whole stellar system, we conclude: 
The attraction of the stellar system on a nebula is not appreciably 
modified by pressure of radiation. Deviations from the law of 
Newton in such nebulae as we have considered, cannot be ace ounted 
for by the counteraction of the pressure of radiation. 
Of course this consideration no longer holds when the dimensions 
of the nebulae become hundreds of times greater. But for the problem 
in question we were obliged to assume that the nebula from which 
the new star is being formed, had already conglomerated to the 
stated dimensions. 
§ 3. The system: nebula-planet. 
In view of some cosmogonic considerations on the origin of the 
solar system, it may be of interest to examine how great the 
pressure of radiation is which can be exerted on a newly formed 
planet by the mother nebula. 
We begin by solving the question: what is the pressure of radia- 
tion which a spherical nebula of constant density @ and radius Rk 
