( 527 ) 



iiivesligcilion I found an iin-liiiiition of Iwo degrees. Eddington in 

 his last investigation, based on tiie superior, newly published, catalogue 

 of Boss, is led to a value of exactly zero degrees. It now api)ears, 

 from the results of the present paper, that both the star-clouds expand 

 in that same plane or at least in directions only slightly deviating. 



It would seem to me tliat we have here a vera causa for the 

 origin of the Milky way. Even if originally the two star-clouds had 

 been spherical and matter had been evenly distributed in them, this 

 matter must have expanded in the neighbourhood of a definite plane, 

 the jilane of the Milky way. 



At the same time, we have at least the l)eginning of an explanation 

 of the two following facts: 



J. That the Milky way has not l)een scattered long ago as a 

 consequence of the divergence in the proper motions of the stars. 

 For, the expansion of matter, now under discussion, must be at work 

 even at the present moment. 



2. That the phenomenon of the Milky way is shown in both the 

 star-streams. 



It is true that Halm and Hough ha>ve assumed, at least for a time, 

 that the Milky way coincided with one of the two streams, but after 

 Eddingtön's work, such a theory seems hardly tenable. 



Our conclusion tacitly assumes that what observation has taught 

 us about the nearer stars, also holds for the more distant ones. If 

 we consider how small the part of the universe is, about which we 

 possess more or less adequate data, we feel that necessarily the 

 bearing of our conclusion is restricted. As applied to the whole 

 system it must necessarily be considered as only a provisional hypo- 

 thesis. In order to give it a more solid foundation, it will have to 

 be based on more ample materials and it will have to be extended 

 to the greatest distances accessible to our observations. 



How necessary an extension over the greater distances is, appears 

 from the fact, that even now a totally ditFerent explanation of the 

 phenomenon has been given. The above residts for the A-stars were 

 not yet known to its author. But it had been evident for some time 

 that, whereas all the other stars investigated show the phenomenon 

 of the two star-clouds, the heliuni-slai's practically move in a single 

 stream. Its motion does not agree with that of one of the two main 

 streams but with the motion of the centre of gravity of the two. 

 This fact led Halm to assume the existence of three streams ^). 

 Eddington "), adopting this theory, conceives the matter to be as 



1) Month!. NoL June 1911. 



2) Observatory Oct. 1911. 



