APRIL 17, 1903.] 



SCIENCE. 



615 



sider that spectroscopic methods are at 

 present capable of discovering only the 

 larger, variations, that very few stars of 

 long periods have probably been advan- 

 tageously observed as yet, and that the 

 velocity of onr sun, due to the orbital 

 motions of the planets attending it, has a 

 double amplitude of only two or three 

 hundredths of a mile per second, there can 

 be no doubt that the number of spectro- 

 scopic binaries must be very great. It is 

 probable that the star unattended by dark 

 companions will be found to be the excep- 

 tion rather than the rule. 



Mr. Wright has computed the orbit of 

 the spectroscopic binary Chi Draconis; 

 Dr. Reese, that of Capella ; Director Camp- 

 bell, that of the variable star and spectro- 

 scopic binary Zeta Geminorum ; and Dr. 

 Crawford, that of Eta Pegasi. 



Dr. Reese investigated the question of 

 the diffraction of light of variable in- 

 tensity, with special reference to the Mills 

 spectrograph, as a guide in designing a 

 more powerful instrument. He has like- 

 wise investigated the cause of the discrep- 

 ancies between measures of spectrograms 

 made with the violet end to the left, and 

 with the violet end to the right, as a result 

 of which he established the purely physio- 

 logical cause of the discrepancy. 



Dr. Reese has also designed a new 

 mounting for the Mills spectrograph. 



Photographs and preliminary measures 

 of several hundred spectra have been made 

 by Messrs. Campbell, "Wright and Reese; 

 and a considerable number of definitive 

 measures have been made. 



In December, 1900, the director utilized 

 the results obtained for the velocities of 

 280 stars situated north of —20 declination 

 in determining the speed and direction of 

 the motion of the solar system through 

 space. The result for the speed of the 

 solar system comes out 19.9 kilometers, or 



12.4 miles per second. The apex of the 

 motion is in R.A. 277° 30', declination 

 +20°. The result for speed is very satis- 

 factory. On account of the absence of ma- 

 terial from the southern hemisphere, and 

 the consequent irregular distribution of the 

 observed stars over the slcy, the direction 

 assigned must be regarded as a rough ap- 

 proximation. 



The average velocity in space of the 280 

 stars is 34.1 kilometers per second. The 

 velocity of the solar system is therefore 

 much less than the average for the other 

 stars. 



Another result of great interest is to the 

 effect that the fainter stars are moving 

 much more rapidly than the brighter ones. 



The velocities of the stars have been ob- 

 served to bear all values between sixty 

 miles approach and sixty miles recession 

 per second. 



Investigations in this line have been 

 shown to be practically endless, by our 

 measurements of the velocity of the star 

 Groombridge, 1830. A special effort was 

 made to measure its velocity, as this is the 

 star which up to three years ago had the 

 largest known proper motion. Its photo- 

 graphic magnitude is in the neighborhood 

 of 7.5. The results obtained have shown 

 that the observations may be extended by 

 present methods to stars perhaps a magni- 

 tude fainter. Stars available for measure- 

 ment are therefore numbered by thousands. 

 As soon as half a dozen of the eight or ten 

 great telescopes now engaged in this work 

 have been made to produce accurate re- 

 sults, it will be highly desirable that the 

 interested observatories arrange and carxy 

 out a scheme of cooperation on a large 

 scale. 



From Mt. Hamilton it is possible to 

 secure the speeds of the stars between the 

 north pole and 30° south declination. The 

 stars in the quarter of the sky from 30° 



