726 
surpasses so much the ‘absorption of an equal mass of scattering 
gas, that by assuming a dust-cloud instead of a gascloud, a moderate 
mass will suffice to account for the observed extinction. In this case 
the absorption does not depend on colour. If a reddening of the stars 
is observed, indicating an absorption through scattering, we may 
still find a moderate mass, if the gascloud is mixed with dust 
particles. This would be in harmony with the views of ARRHENIUS, 
who has found in his studies on cosmogony that the small particles 
in space, driven away by lightpressure, are caught and collected 
in the extensive world nebulae. 
