ASTRONOMY: F. H. SHARES 
521 
-/*S'-t30 -//O" -so" -70" -so' -so" -/CT O ♦/O' *SO' fSO' 1-70' *90' tllO' *I50' 
FIG. 5. 
Maanen finds for Messier 101 an annual rotational component of 0.022 
for a distance of 5' from the center. Combining this with the rotational 
velocity of 330 km. per sec. for a distance of 2' gives 0.00013 for the par- 
allax of N. G. C. 4594. The result is of the same general order as that 
found by Curtis for spiral nebulae as a class from a discussion of their 
proper motion.^ 
^Aslroph. /., 15, 287 (1902). 
■'Lick Obs. BiilL, 278 (1916); Puh. Astr. Soc. Fac., 28, 119-20 (1916). 
^Leipzig, ViertcljSchr. astr. Ges., 49, 162 (1914). 
*Ibid., 50, 97 (1915). 
^ Van Maanen, these Proceedings, 2, 386, July 1916. 
'^Pop. Astr., 23, 21 (1915). 
' Pub. Astr. Soc. Pac, 27, 217 (1915). 
A SIMPLE METHOD FOR DETERMINING THE COLORS OF 
THE STARS 
By Frederick H. Scares 
MOUNT WILSON SOLAR OBSERVATORY. CARNEGIE INSTITUTION OF WASHINGTON 
Received by the Academy, July 24, 1916 
Aside from visual estimates, such as those by Miiller and Kempf 
in the Potsdam Durchmusterung, three methods of determining the 
colors of stars have been more or less widely apphed. The earliest of 
