ASTKONOMY. 127 



There is only a rougii sort of agreement, but all three unite in 

 placing the apex considerablj- in advance, in right ascension, of the 

 apex as found from the proper motions of stars by Struve, Airy, Dun- 

 kin, and others (the mean position generally assigned is, K. A. 200° 5 

 Decl. +35°), while Struve found a velocity of translation of only 

 about 4J miles per second. 



Herr Homaun is inclined to think that the velocity of translation of 

 the sun does not differ very much from the velocity of the earth in its 

 orbit, that is, 18^ miles per second. Dr. von Kovesligethy in 1883 found 

 from spectroscopic observations that the rate of motion of the solar 

 system was 8.G geographical miles per second. The spectroscopic ob- 

 servations were insufficient to determine the direction, and he assumed 

 the apex in E. A. 216o.O, Decl. +35°.!. 



Dr. Ubaghs, of Liege, in making a preliminary examination of the 

 aberration due to the motion of the solar system, pointed out by M. 

 Folic, has obstained a result which would give a velocity of only about 

 180 feet per second. 



The velocity of light and the solar parallax. — Professor Newcomb has 

 published in vol. 2 of the "Astronomical papers prepared for the use 

 of the American Ephemeris" the details of his researches on the velocity 

 of light, made during the summer mouths of 1880, 1881, and 1882. The 

 apparatus used, to which the name " photo-tachometer" has been given, 

 is a modified form of Foucault's revolving mirror. The result obtained 

 for the velocity of light in vacuo is 299,860 kilometers, or 186,3i7 miles 

 per second, with a probable error of 30 kilometers. Michelson found 

 in 1879 a velocity of 299,910 kilometers, and repeating his work at Cleve- 

 land in 1882, he obtained 299,853. Accepting the value 299,860 as the 

 true one, it becomes of interest to consider the value thereby deducible 

 for the parallax and distance of the sun. The latest and probablj^ the 

 most accurate -determination of the constant of aberration is that of 

 Dr. Nyren, 20".492. Combining this with the above velocity of light and 

 Clarke's value of the earth's equatorial radius (6,378.2 kilometers), we 

 obtain 8". 791 for the value of the solar parallax, almost exactly the same 

 as that obtained from heliometer observations of Mars in 1877. The cor- 

 responding distance of the sun is 92,960,000 miles. 



With regard to a possible difference between the velocities of rays of 

 different colors, it is pointed out that the phenomena of variable stars 

 seem to be conclusive against the hypothesis of any such difference. 

 Were there a difference of one hour in the times of the blue and the red 

 rays reaching us from Algol, this star would show a well-marked color- 

 ation in its phases of increase and decrease. No such effect, however, 

 has been noticed. Recent researches by Professors Michelson and Mor- 

 ley have led to a similar result. 



Transits of Venus 1874 and 1882.— The work of the United States 

 Transit of Venus Commission is being rapidly carried to completion 



