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SUMMARY. 
After having adduced some grounds in $ 1 why it seems desirable 
to study the effect of pressure of radiation in nebulae, we examined 
the system nebula-star in $ 2. In this case the value of the pressure 
of radiation remains so small that even under favourable conditions 
no effect can be expected. Treating in § 3 the system nebula-planet, 
we saw that it is not excluded that in the first time of their for- 
mation from solar nebula the large planets were subjected to a 
strong pressure of radiation, and this may perhaps be responsible 
for some peculiarities in the system. 
In the investigation of the system formed by two or more nebulue 
in § 4 we came to the conclusion that if anywhere, the pressure 
of radiation must manifest itself here. 
Bussum, April 1921. 
