162 . HISTOKY OF ASTRONOMY. 



gold medal of the Koyal Astronomical Society of Lon- 

 don, for this important discovery. The parallax of 61 

 Cygni, according to these observations, is 0".348, making 

 the distance of this star from the sun 592,000 times the 

 radius of the earth's orbit a distance which light would 

 require more than nine years to traverse. 



This result has received confirmation from the re- 

 searches of M. Peters, who from a series of zenith dis- 

 tances of the star, determined at the observatory of Pul- 

 kova during the years 1842 and 1843, has found its paral- 

 lax to be equal to 0".347. These observations were made 

 with the grand vertical circle of Ertel, which is 43 inches 

 in diameter, graduated to 2 minutes, and reading by four 

 microscopes to one tenth of a second. 



A series of observations of 61 Cygni have also been 

 made by Mr. Johnson, with the new heliometer of the 

 Oxford observatory. These observations were com- 

 menced in 1852 and were continued through the years 

 1853 and 1854, and they fully confirm the fact of an 

 annual parallax, very nearly of the same amount as that 

 found by Bessel. The stars selected for comparison were 

 different from those which Bessel used, both stars lying 

 nearly in the direction of the components of 61 Cygni. 

 These observations give the parallax 0".392 or 0".402, 

 according as a temperature correction is applied or not. 



M. Otto Struve, of the Pulkova observatory, has made 

 some observations of 61 Cygni with a wire micrometer 

 attached to his telescope, and a preliminary calculation 

 has furnished for the parallax 0".52, a result sensibly 



