ON ASTEONOMY. 



135 



the discussion of his observations, on which, as Herschel remarks, 

 " every imaginable cause of disturbance was taken into careful con- 

 sideration and its effects rigorously calculated," he reached the con- 

 clusion that the parallax of Gl Cygni was 0".348. 



From this we infer that light would reach us from this star in 9\ 

 years. This result of Bessel has received the most ample confirmation 

 by Peters of Pulkowa, who, in a series of observations, made in 1842 

 and 1843, with consummate address in the use of every refinement 

 which could insure accuracy, found the parallax of this same star to 

 be 0".349, differing from the result of Bessel by only the yoVo of ^ 

 second. Such a coincidence between the results of different observers, 

 with different instruments and in different places, cannot but inspire 

 great confidence in the conclusion to which they have come. 



The star a Centauri, the brightest star in the southern constellation, 

 has been much observed with a view to its parallax ; first by Hen- 

 derson in 1832 and 1833, then by Maclean in 1839 and 1840, and 

 again in 1848, both at the Cape of Good Hope. The mean of the 

 results gives for the parallax of this star 0".915, which places it nearer 

 to our system than any star whose parallax has been determined. 

 And yet light would be nearly four years in coming from this our 

 nearest stellar neighbor. 



The parallaxes of the following stars have been proximately de- 

 termined. I give them in a tabular form, with their parallax, the 

 name of the observer, and the number of years required for light to 

 come from the star to us : 



stars. 



a Centauri 



Do 



Gl Cygni 



a Lyrae 



Sirius 



1830 of Groombridge's Catalogue 



I UrsEe Majoris 



Arcturus 



Polaris 



Capella 



Parallax. 



0.915 

 0.918 

 0.348 

 0. 2G1 

 0.230 

 0. 226 

 0. 133 

 0. 127 

 0. 067 

 0. Oi6 



Observers. 



Henderson . 



Maclean 



Bessel 



Struv^ 



Henderson. 



Peters 



...-do 



...-do.. 



.--.do.. 



.-..do.. 



Years. 



3.6 



9.4 

 12.6 

 21.9 

 22. 

 24.8 

 2.5.9 

 31. 1 

 71.7 



The parallax bears no definite ratio to the magnitude of the star. 

 The severest scrutiny of the bright star a Cygni, by the powerful in- 

 struments of Peters, shows absolutely no indication of any measurable 

 parallax. 



We can now give at least a partial answer to the question, how far 

 off are the stars? An infant is born, and at the same time a beam of 

 light starts from the bright star in the Swan on its way to our distant 

 world. Tiie child pas.ses through the slow-recurring stages of life, 

 reaches manhood and old age, and lingers his fall century and dies ; 

 and the light has not yet reached us ! Such is the distance which we 

 vainly try to contemplate. 



