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PRESS OF THE NEW ERA PRINTING COMPANY

LANCASTER PA

CONTENTS.

258856

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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 distances 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, 1912.

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