Astronomical Operations at the Pulkova Observatory. 91 



Brinkley found the constant of nutation to be 9''-25 and Rob- 

 inson 9'' -24. The mean of the two preceding values of the par- 

 allax of the pole star is very nearly 0''-16, or a httle less than a 

 sixth of a second, which would correspond to a distance of this 

 star from the earth a little more than double of that of 61 Cygni, 

 (as determined by Bessel,) or nearly to thirteen hundred thou- 

 sand times the mean radius of the earth's orbit. Struve found 

 the parallax of « Lyrae to be 0"-2613, with a probable error of 

 C-0254 ; from which it results that the distance of this star is 

 771400 times the mean radius of the earth's orbit, a space which 

 would require twelve years for the light to pass through ; while 

 it would require more than twenty yeai-s for light which moves 

 at the rate of 192500 miles per second to travel from the pole 

 star to the earth. 



Respecting the coefficient of aberration of the fixed stars, 

 Struve has obtained a new value of it, by a complete discussion 

 of the observations made by himself at Pulkova from 1840 to 

 1842, with the transit instrument already mentioned, established 

 in the prime vertical. The general result of the observations of 

 seven stars near the zenith, gives for the aberration 20'''-4451, 

 with a probable error of only O'-'-Olll. The extreme values of 

 the means arising from observations of different stars are 20''''3947 

 and 20'^-5036. From the smallness of these differences, Struve 

 concludes that we must admit the same constant of aberration, 

 that is, the same velocity of light in these seven stars. 



The velocity of light which results from the preceding value 

 of the aberration by adopting the parallax of the sun obtained 

 by Encke, and the dimensions of the terrestrial spheroid accord- 

 ing to Bessel, is 69197 leagues of 25 to the degree, in a second 

 of mean time, with a probable error of 38 leagues. The time 

 which light employs in passing over the mean distance of the 

 sun and earth is 8' 17''-78, with a probable error of 0'^-27. 



Mr. Otho Struve has performed a laborious calculation in order 

 to estimate numerically the constant of the precession of the 

 equinoxes, taking into account for the first time the proper mo- 

 tion of the centre of gravity of the solar system in space. 



Bessel, in order to determine the constant of precession, had 

 compared the catalogue deduced by himself from Bradley's ob- 

 servations for 1755, with that of Piazzi, and had thence concluded 

 for the general annual precession in 1790, the value at present 

 admitted, viz. 50'''32106. 



