MOUNT WILSON SOLAR OBSl^RVATORY. 175 



According to the latest determination by Eddington, the numbers of stars 

 contained in the first and second streams are in the ratio 3 : 2 for the second 

 type stars, but 3:1 for the early A stars. The second stream, therefore, 

 becomes relatively poorer the earlier the type of spectrum. It seems reason- 

 able to conclude that the fact that almost all the stars of the Orion type, the 

 earliest type of all, seem to belong to a single stream, must be due to the 

 extreme poverty of the second stream. Since, however, it seems reasonable 

 to expect that some traces of this stream must still exist, a careful search 

 has been begun for stars which may belong to it. Partial success has 

 already been obtained. There can hardly be any doubt that such Orion stars 

 as 165 G Canis Majoris, uHcrculis, Groombridge 2533, 12 Lacertce, and 58 

 Pegasi, must belong to the second stream. As a definite conclusion can not 

 in most cases be reached without a determination of the radial velocities, the 

 search must necessarily proceed somewhat slowly. 



At the present time the further probable results of the whole investigation 

 may be summarized as follows : 



As we pass from the stars of the solar type to those of type A and thence 

 to the Orion stars, 



(i) The parallelism of the motion of the stars in each of the two streams 

 becomes more marked. 



(2) The direction of the stream-motion, relative to the sun, changes 

 gradually. 



(3) The velocity of the stream-motion, relative to the sun, decreases 

 gradually. 



(4) The number of stars in the second stream, as compared with that in 

 the first, decreases. 



The certainty of these conclusions depends of course upon the reliability 

 of the observational data on which they rest, and these, up to the present 

 time, are for the most part very meager. For this reason a large number of 

 stars of the Orion type and type A have been added to the radial velocity 

 program of the 60-inch reflector. Should the data which we may expect to 

 secure in a short time with this instrument confirm the provisional results 

 given above, we shall learn some very significant facts as to the amount and 

 direction of the relative motion of the two star-streams, facts which in turn 

 promise to throw some light on the question of the origin of the two streams 

 and that of the Milky Way itself. 



' In addition to the work upon the Orion and A type stars. Professor 

 Kapteyn has devoted some time to working out parts of the program of the 

 60-inch reflector, giving especial attention to observations for the determina- 

 tion of the absorption of light in space. 



At the request of Professor Kapteyn, Mr. Fath has been continuing 

 throughout the year observations on the average brightness of different por- 

 tions of the sky. In addition Mr. Fath has obtained with a low-dispersion 

 spectrograph loaned by Director Campbell, of the Lick Observatory, two 



