per second for the early type (young) stars to 

 about 20 kilometers per second for the late type 

 (old) stars. Boss, whose meridian-circle obser- 

 vations in the northern and southern hemispheres 

 have determined the positions of numerous stars 

 with the highest precision, deduced a similar con- 

 clusion from his studies of stellar motions perpen- 

 dicular to the line of sight. The meaning of this 

 remarkable variation of velocity with type is not 

 yet understood and it will remain for future re- 

 searches on the fainter stars to develop its full 

 significance. 



Although the average velocities of stars are thus 

 found to be moderate, notable exceptions are fre- 

 quently encountered in the work with the 6o-inch 

 reflector. Among the high velocities in space thus 

 far found on Mount Wilson, cases of 141, 150, 179, 

 233, 316, and 320 kilometers per second may be 

 mentioned. The last-named is the highest velocity 

 of translation yet found for any star. At these 

 speeds the attraction of the entire known stellar 

 system would be wholly insufficient to check the 

 star in its flight into unknown regions of space. 



SPECTROSCOPIC BINARIES. 



Pickering was the first to discover a to-and-fro 

 shift, in a definite period, of the lines in the spectra 

 of certain stars. He attributed it to orbital mo- 

 tion, and thus the possibility of detecting "spec- 

 troscopic binaries" was shown. These are double 

 stars lying too close together to be separately dis- 



