482 



NA TURE 



[October 7, 1922 



A Fifty-foot Interferometer Telescope. 1 



By Dr. George E. Hale. For.Mem.R.S. 



THE angular diameter of a star was measured for 

 the first time by Mr. Francis G. Pease at the 

 Mount Wilson Observatory on December 13. 1920. 

 with a 20-foot Michelson interferometer attached to 

 the 100-inch reflecting telescope. The method em- 



21,000,000, 270,000,000, and 400,000.000 miles re- 

 spectively. These stars are all in the giant stage, with 

 densities ranging from o-oooooi (Antares) to 0-0002 

 (Arcturus). The Sun, a dwarf star 866,000 miles in 

 diameter, in a much more advanced state of develop- 



ploved is due to Prof. Michelson, who had adjusted j ment, has a density of 1-4 (water =1) 



Fig. 2 

 Model seen froi 



the interferometer and tested it on stars during the 

 previous summer, with the assistance of Mr. Pease. 

 Since that time Mr. Pease has measured the diameters 

 of Betelgeuse, Arcturus, Aldebaran, and Antares. On 

 the basis of the best available values of their parallaxes, 

 the corresponding linear diameters are 215.000.000. 



1 The substance of this article was communicated to Section A of the 

 British Association at Hull on Monday, Sept. II, by Prof. H. H. Turner, 

 who showed the photographs of the model on the screen. 



It would evidently be of great interest to measure 

 the diameters of other stars, of various spectral types, 

 because of the direct bearing of the results on the 

 problem of stellar evolution. Unfortunately, very few 

 are within the range of the 20-foot interferometer, and 

 neither the capacity of the telescope mounting nor the 

 width of the observing aperture in the dome will permit 

 a larger instrument to be used with the 100-inch re- 



NO. 2762, VOL. I 10] 



