69 
The value of S is still a doubtful point. 
If we should assume that the nebula emits black radiation, S 
would already be = ssp at a mean temperature of not quite 1500°, 
hence attraction and repulsion would be about equally great. 
This is undoubtedly erroneous; the radiation has been smaller 
than is calculated on the strength of STrPHAN-BOITZMANN’s law. On 
the other hand the nebula will have emitted other radiation *) 
besides temperature-radiation, which again partly compensates the 
deficit. 
In our opinion the result of this research may, therefore, be 
summarized as follows: 
On account of the uncertainty which prevails with regard to the 
quantity of energy emitted by the nebula, it is difficult to make an 
accurate estimation of the amount by which the attraction of the 
mother nebula on a newly separated planet must be diminished in 
virtue of the pressure of radiation. In consequence of the contraction, 
both of planet and of nebula, the effect in question will continually 
diminish, and in general it will also have been greater for the larger 
and more remote planets. Taking everything together it is not ewcluded 
that the said diminution, had a quite appreciable amount, at least 
for the large planets. 
If, therefore, in our solar system particularities should occur 
which can be accounted for as the result of such a change of gra- 
vitation, there is every reason to accept this explanation. And this 
seems actually to be the case, among others with the small inclina- 
tions and small eccentricities of the large planets. (See among others 
Nörke loc. eit). To enter more fully into this, would lead us too far. 
§ 4. Gravitation and pressure of radiation in a nebula. 
Departing from our considerations in the preceding $$ we shall 
now consider the more irregular nebulae, which present two or more 
condensations, as e.g. the Dumbbell nebula. Most nebulae have 
dimensions which are probably to be measured in thousands of 
Neptune orbit radii. Not much is known about their masses. But 
when we assume that a multiple star will be formed out of such 
a nebula, we must assign to each of the parts of the nebula a mass 
of the same order of magnitude as our sun has. In order to effect 
a rough estimation of the acting forces, we shall more fully discuss 
the following system. 
1) The light of the tails of comets, and probably of most nebulae, arises besides 
through temperature radiation, through other processes, which are not yet entirely 
known. 
