220 CARNEGIE INSTITUTION OF WASHINGTON. 



SPECTRA OF NEBULAE. 



Mr. Pease has also photographed with the same spectrograph the 

 spectra of the planetary nebulae N. G. C. 6210, 6543, and 7009, and 

 two points in the irregular nebula N. G. C. 7023. 



Professor Kapteyn's Investigations. 



Professor Kapteyn has devoted most of his attention to a further 

 study of the helium and early A stars. During the last two or three 

 years the work has necessarily been of a preliminary character. In 

 consequence of this fact the accounts which have appeared from time 

 to time* have also been simply preliminary communications. Now 

 that observations for radial velocities of the helium and A stars at the 

 Mt. A\ilson Solar Observatory are nearing completion, it is intended 

 to bring these investigations to a more or less definitive close. 



A first paper, which is almost ready for press, will treat of the 

 helium stars in Boss's "Preliminary Catalogue," between galactic 

 latitudes ±30° and longitudes 217° to 360°. Their number is 319, 

 which is about half of all the helium stars between these latitudes and 

 somewhat over 42 per cent of the helium stars in Boss's catalogue. 

 Fourteen of these stars seem to belong to a separate group — the Vela 

 group — and one probably to the second stream. With few excep- 

 tions—mostly near the limits — all the rest apparently belong to a 

 single group. Considerable care was taken to put this point beyond 

 reasonable doubt. Of the 304 stars, 21 were finally considered as 

 exceptions and were consequently rejected. Of course there remains 

 some doubt whether a few other stars ought not to be counted as 

 members of the group, but such uncertainty seems unavoidable. 



For each of the 283 stars admitted to the group the parallax was 

 derived by a method similar to that employed by several astronomers 

 for the members of the Vela group and the Hyades. The probable 

 errors for each of these parallaxes were also computed. In general 

 the accuracy is satisfactory and a first attempt to draw up a star-map, 

 showing the positions of the stars in space, thus appeared to be justi- 

 fied. As the publication of the paper will soon follow, further par- 

 ticulars need not be given here. 



At the request of the Director a short paper has been prepared, 

 bringing together, in the briefest possible space, the evidence we pos- 

 sess at present as to the reality of the two following phenomena : 



(a) On the average the fainter stars are redder than those that 

 are brighter. 



*0n the Systematic Proper Motions of the Orion Stars (Transactions of the Interna- 

 tional Union for Cooperation in Solar Research, 3, 215, 1910). Een paar nieuwere 

 onderzoekingen op het gebied der evolutie van de vaste sterren en het sterrenstelsel 

 (Address before the Congress of Physicists and Physicians in the Netherlands, April 1911). 

 The Milky Way and the Star-Streams (Meeting of the Academy of Sciences in Amsterdam, 

 December 1911). Star Systems and the Milky Way (Meeting of thcAcademyof Sciences 

 in Amsterdam, February 1912). On the Structure of the Universe (Address before the 

 National Academy of Sciences at Washington, April 1913.) 



