ASTRONOMY: H. SHAPLEY 
479 
erosion; and the occurrence of such forms beneath heavy Hmes tones, 
600 feet or more in thickness, clearly demonstrates the submergence 
of a previously eroded volcanic mass by over 600 feet, while the lime- 
stones were forming. Thus not only the recent history of the present 
barrier reef around Vanua Mbalavu, but also the Pleistocene history 
of the now dissected almost-atoll, of which Vanua Mbalavu is a remnant, 
testifies unquaUfiedly in favor of Darwin's theory of coral reef and 
against all other theories. [Since the above was written Foye^ gives 
independent evidence of the eastward tilting of Lakemba, which is on 
about the same meridian as Vanua Mbalavu.] 
1 J. S. Gardiner, Cambridge, Eng., Proc. Phil. Soc, 9, 1898, (417-503). 
2 A. Agassiz, Cambridge, Mass., Bull. Mus. Comp. Zool., Harvard Coll. 33, 1899, (1-167). 
» W. G. Foye, Amer. J. Sci., New Haven, 43, 1917, (343-350). 
STUDIES OF MAGNITUDE IN STAR CLUSTERS, VII. A METHOD 
FOR THE DETERMINATION OF THE RELATIVE 
DISTANCES OF GLOBULAR CLUSTERS 
By Harlow Shapley 
MOUNT WILSON SOLAR OBSERVATORY. CARNEGIE INSTITUTION OF WASHINGTON 
Communicated by G. E. Hale. June 9. 1917 
Mor^ than 150 variables for which the light changes are rapid and 
periodic have been found among the thousand brightest stars in the 
globular cluster Messier 3. Eighty per cent of them were discovered 
twenty years ago by Professor Bailey at Harvard/ and the remainder 
three years ago by the writer at Mount Wilson The light variations 
of these st^rs are typical of a large class of variables — the short period 
Cepheids — some of which are found among the stars in the sky at large, 
though the far greater majority of those now on record are confined to 
a few of the globular clusters and to the Magellanic clouds. Wherever 
found they appear remarkably alike in range of variation, spectral 
type, color variation, length of period, nature of light changes, and 
even in the irregularities of the periods and the fluctuations of the light 
curves. 
Recent work with the 60-inch reflector on the variables in Messier 3 
is supplemental to the determination of light curves and periods by 
Bailey ,3 and is incorporated in the general study of magnitudes in clus- 
ters primarily for the intercomparison, on the basis of the Mount Wilson 
scale of magnitudes, of the brightness of variables in this and other 
globular systems. It is part of an investigation of the magnitudes and 
colors of all the brighter stars in Messier 3, and follows the methods 
previously employed.'* 
