188 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



approximately equal size tlian the sun and the planets. The motions 

 of a considerable number of these spectroscopic binaries have been 

 investigated by mathematicians, and the orbits of the motions have 

 been determined, but there still remains a large number of them for 

 which this information is not yet available. These latter objects 

 were rejected from Prof. Campbell's general discussion of the stellar 

 motions on account of tlie indefiniteness which must attend their 

 motions for a time. There are besides a considerable number of stars 

 Avhose spectra are so vague and difficult to measure that the results 

 from them are uncertain. Accordingly, there remained available for 

 his investigation only about 1,200 objects. 



The first investigation relates to the motion of the solar system in 

 space. As in a forest walk the trees in front seem to separate as we 

 approach and those behind to come together as we recede, so the stars 

 to the telescopic observer would appear to crowd toward the point 

 of the sky from which we are receding and to separate from that 

 point of the sky toward which we are approaching, if the sun with 

 the planets is in motion in the heavens with respect to the positions 

 of the stars. Such tendencies were noted by Sir William Herschel 

 in 1783, from a consideration of the proper motions of 13 stars, all 

 then available. He found that the solar system was traveling ap- 

 proximately toward the star X Hercules, in right ascension 262°, 

 declination, +26°. 



The information found by the spectroscope relates to motion at 

 right angles to that which is observed by the telescope, so that while 

 the telescopic observer would find the stars precisely in the solar 

 apex to have no component of motion caused b}?^ their relations to 

 the solar system, the spectroscopic observer would find these stars 

 to be approaching the earth with the maximum velocity, while those 

 at the opposite point would be receding from the earth with the same 

 velocity. The telescopic observer, looking at right angles to the 

 line of motion of the solar system, would see the stars at the maxi- 

 mum velocity^ whereas the spectroscopic observer, looking in the 

 same direction, would find no radial velocity at all caused by the 

 solar motion. 



Director Campbell's general solution for the solar motion derived 

 from all the stars investigated, 1,193 in number, gave the following 

 values: Apex at right ascension, 268°.5, declination -1-25°. 1, and 

 velocity 19.5 kilometers per second. 



In Prof. Lew^is Boss's discussion of the proper motions of 6,188 

 stars, he also has derived the position of the apex toward which 

 the solar system is approaching. He finds it in right ascension 

 270°. 52, declination -f34°.28, and he finds that for stars situated at 

 90° from the apex, which of course, will show the greatest apparent 

 velocity of recession from the apex, the mean rate of apparent mo- 



