DOUBLE STARS. 207 



most recent gives one ninth, as the proportion of the cosmic- 

 al bodies which, by an observed motion both of the primary 

 star and the companion, are manifestly proved to be phys- 

 ically double stars. 



Very little has as yet been numerically determined re 

 garding the relative distribution of the binary star-systems 

 throughout space, not only in the celestial regions, but even 

 on the apparent vault of heaven. In the northern hemi- 

 sphere, the double stars most frequently occur in the direc- 

 tion of certain constellations (Andromeda, Bootes, the Great 

 Bear, the Lynx, and Orion). For the southern hemisphere 

 Sir John Herschel has obtained the unexpected result, "that 

 in the extra-tropical regions of this hemisphere the number 

 of multiple stars is far smaller than that in the correspond- 

 ing portion of the northern." And yet these beautiful south- 

 ern regions have been explored, under the most favorable 

 circumstances, by one of the most experienced of observers, 

 with a brilliant twenty-feet reflecting telescope, which sep- 

 arated stars of the eighth magnitude at distances even of 

 three quarters of a second.* 



The frequent occurrence of contrasted colors constitutes an 

 extremely remarkable peculiarity of multiple stars. Struve, 

 in his great workf published in 1837, gave the following re- 

 sults with regard to the colors presented by six hundred of 

 the brighter double stars. In 375 of these, the color of both 

 principal star and companion was the same and equally in- 

 tense. In 101, a mere difference of intensity could be dis- 

 cerned. The stars with perfectly different colors were 120 

 in number, or one fifth of the whole ; and in the remaining 

 four fifths the principal and companion stars were uniform in 

 color. In nearly one half of these six hundred, the princi- 

 pal star and its companion were white. Among those of 

 different colors, combinations of yellow with blue (as in i 

 Cancri), and of orange with green (as in the ternary star y 

 Andromedae),t are of frequent occurrence. 



Arago was the first to call attention to the fact that the 

 diversity of color in the binary systems principally, or at least, 

 in very many cases, has reference to the complementary col- 

 experiments with very complicated systems have confirmed the astron- 

 omer in the hope that these estimates are mostly correct within 0"'l 

 (Strnve, iiber Doppelsterne nach Dorpater Beob., B. 29.) 



* Sir John Herschel, Observations al tht Cape, p. 166. 



t Struve, Mensurte Microm., p. Ixxvii. to Ixxxiv. 



t Sir John Herschel, Outlines of Aslr., p. 579. 



