PROCEEDINGS 



OF THE 



AMERICAN PHILOSOPHICAL SOCIETY 



HELD AT PHILADELPHIA 

 FOR PROMOTING USEFUL KNOWLEDGE 



Vol. LI January-March, 1912 No. 203 



DETERMINATION OF THE DEPTH OF THE 



MILKY WAY. 



By T. J. J. SEE. 

 {Read January 5, 1912.) 



Introductory Remarks. 



The problem of determining the depth of the Milky Way, as 

 accurately as possible, is one which has now engaged my attention 

 for over twenty years, and I will therefore take this occasion to 

 bring together the results at which I have arrived, partly because 

 they are of high general interest, and partly because the progress thus 

 made will prove instructive as to the methods which must be 

 adopted for the measurement of the distances of the most remote 

 objects of the sidereal universe. Here we have to deal with dis- 

 tances so immense that the method of annual parallaxes, commonly 

 used for the stars comparatively near the sun, utterly fails; and 

 recourse must be had to other methods which will serve for the 

 greatest distances to which our modern giant telescopes can penetrate. 



Alpha Centauri, the nearest of the fixed stars, was also the first 

 to be successfully measured for parallax, by Thomas Henderson, of 

 the Cape of Good Hope, in 1831 ; but the work was not reduced till 

 January, 1839, and meanwhile Bessel had measured the parallax of 

 61 Cygni in 1838 and promptly published the result of his triumph. 



PROC. AMER. PHIL. SOC. , LI. 203 A, PRINTED MARCH 16, I9I2. 



