April 17, 1903.] 



SCIENCE. 



613 



numerous. It is not too much to say that 

 their discoveries and observations of new 

 double stars, and their measures of known 

 double stars, outnumber several-fold the 

 corresponding output of all other observa- 

 tories in the past two years. Both ob- 

 servers have devoted a portion of their 

 time to the discovery of new pairs. Mr. 

 Hussey has found 312 systems in the past 

 two years, and 564 since 1898. They may 

 be classified as follows: 



The corresponding discoveries by Mr. 

 Aitken have been 249 since July, 1900, and 

 345 since 1898, as follows : 



Distances between 0".00 and 0".25, 20 pairs. 



.26 " .50, 55 " 



.51 " 1 .00, 78 " 



1 .01 " 2 .00, 91 " 



2 .01 " 5 .25, 101 " 



Total ~345 " 



By way of explanation, it should be said 

 that in general the closer the components 

 of a pair the more interesting and impor- 

 tant it is. The majority of stars in which 

 orbital motions have been detected are 

 closer than 1". Up to the present time 

 about 1,500 double stars with distances 

 under 1" have been discovered at all the 

 observatories. More than one third of 

 these have been found at the Lick Observa- 

 tory, and more than one fourth of the 

 whole number have been discovered here 

 within the last three years. 



Many interesting results have come from 

 the systematic observation of the well- 

 known interesting pairs. Of these, the 

 most striking case is Delta Equulei. It was 

 supposed that its period of revolution was 

 eleven and four tenths years — surpassed in 

 rapidity of motion only by Kappa Pegasi, 



period eleven and one third years. In the 

 fall of 1900 it was noticed by Mr. Aitken 

 that the components of Delta Equulei were 

 not following the paths marked out for 

 them by the orbit hitherto accepted as 

 substantially final. Mr. Hussey investi- 

 gated the question of their orbit, making 

 use of all the known observations. He 

 came to the conclusion that the chances 

 were greatly in favor of a period only one 

 half the length of that previously assumed, 

 namely, five and seven tenths years. Sys- 

 tematic observations by Messrs. Hussey and 

 Aitken during the past year have estab- 

 lished the correctness of this view. The 

 period of this interesting binary is fifty 

 per cent, shorter than that of any other 

 known double star. Observations of this 

 system obtained with the Mills spectro- 

 graph are in harmony with Mr. Hussey 's 

 theory. 



Mr. Hussey has also in the past two 

 years secured 1,899 observations of W. 

 Struve, Otto Struve, miscellaneous and 

 new doubles. 



Mr. Aitken has obtained 1,431 observa- 

 tions, his observing list being mainly com- 

 posed of known rapid binaries, and other 

 close and difficult pairs. He has likewise 

 computed orbits for 99 Herculis, Zeta 

 Sagittarii and Beta Delphini. 



Mr. Hussey completed his observations 

 and discussions of the Otto Struve Double 

 Stars, and his work was issued in the sum- 

 mer of 1901 as Volume V., 'Publications 

 of the Lick Observatory.' 



The Crossley Eefleetor has been busy on 

 practically every good night. In addition 

 to the observations already referred to, 

 Messrs. Palmer and Dall made thirty-three 

 exposures on the nebulse contained in Pro- 

 fessor Keeler's program, in the first half 

 of 1901. Mr. Perrine has since secured 

 twenty-three exposures on these nebulee, 

 twenty-eight exposures on the Rumford 



