[king] molecules in INTERSTELLAR SPACE 103 



ones (Lindemann's estimate is 4,000),^° the ratio referred to is still 

 very large. 



It is evident that unless this "residual" or "primordial" gas is 

 exempt from mutual gravitation^^ it must give rise to a gravitational 

 field very much greater than that of the whole sidereal universe and 

 should therefore be taken into account in existing theories of stellar 

 dynamics. Although the dynamics of such a system would probably 

 have to be modified to a considerable extent to take into account 

 radiation pressure, we should still expect an enormously high density 

 near its mass-centre, unless the whole be endowed with a small angular 

 velocity as is surmised to be the case with the Milky Way. 



It follows from this brief discussion that we are either obliged 

 to accept the existence of a wide-spread distribution of enormous 

 quantities of interstellar gas of molecular density of the order 10^ 

 molecules per cm.^ and take into account its influence in stellar 

 dynamics, or conclude that the attenuation of light by scattering is 

 very much less than is indicated by existing estimates of the absorp-' 

 tion of stellar radiation in space. 



McGill University, Montreal. 



20 Lindemann, F. A., "Note on the Number of Dark Stars," Monthly Notices, 

 75 (1915). 



2^ On this point note a remark by Eddington, loc. cit., p. 258. 



