14 PROCEEDINGS OF THE AMERICAN ACADEMY 



The search for a star with a very small parallax seems more hopeful, 

 since it could not have been detected by other measures. 



The observation would have value if we could determine the direc- 

 tion of the motion, even if we could not measure its amount, since 

 it would show which portion of the orbit was turned towards the 

 observer. This cannot be found from the micrometric measurements, 

 since, although we can obtain from them the amount of the inclina- 

 tion, we cannot determine its sign. 



It is also possible that some method of greater delicacy may be dis- 

 covered, so that the spectroscope may be replaced by a more sensitive 

 instrument, as it has been by the interferential refractometer in 

 measuring the index of refraction of gnse^. 



The semi-axes major of 2 3121, 1768, 22G2. and 2055 are not given 

 in the original publications of the orbits. The values inserted in 

 Table V. are those given in the Handbook of Double Stars, by 

 Messrs. Crossley, Gledhill, and Wilson. This work has also proved 

 most useful in various ways in the preparation of this paper. The 

 value of a given by Dr. Auwers for a Canis Majoris is 2.33. This 

 relates to the ellipse described by the bright star. As the companion 



is assumed to have a mass — times as great as this, the value of a 



must be multiplied by 3.05, and therefore 2.33 X 3.05 = 7.11 is the 

 value adopted. It is obvious that for this star the intrinsic bright- 

 ness of the two components is by no means the same. If the 

 density is the same, the diameter of the companion would be 

 0.79 that of the primary. The area of its disk would be 0.62, 

 while its light* is only 0.0001 of that of its primary. The very 

 large relative diameter of y Leonis is remarkable. Its brightness 

 must be about three hundred times that of the Sun, if it-* density is 

 the same. On the other, hand, if no brighter tlian the Sun, its 

 density would be only one seventh of 'that of attnosphorie air at the 

 standard density and pressure, to give it a sufficient bulk to emit its 

 ol)served light. If the other binaries have the same density as the 

 Sun, their brightness must vary from 100 in the case of c^ Ci/f/nt to 

 0.06 in the case of p Eridani, the brightness of the Sun bi-ing taken 

 as the unit. The semi-axis major and period of 61 Ci/gni are taken 

 from Newcomb and Ilolden's Astronomy. Although this star is com- 

 moidy regarded as a binary, the evidence in favor of this view seems 

 to depend upon the large proper motion of both components, and the 

 fact that both appear to be comparatively near the Sun. It is doubt- 



♦ Ann. Ilarv. Coll. Obscrv , xi. 177. 



