XII 



HUMBOLDT S CORRECTIONS AND ADDITIONS. 



eaid, The time which elapses between the moment in which the plane 

 tary secondary star is nearest to the Earth, and that in which it is most 

 distant from it, is always longer when the star passes from the point of 

 grsatest proximity to that of greatest elongation, than in the convers^, 

 when it returns from the point of greatest elongation to that of greatest 

 proximity. 



Page 213, line 1. 



In the French translation of the astronomical volume of the Cosmos^ 

 which to my gi-eat gratification, M. H. Faye has again undertaken, this 

 learned astronomer has much enriched the section upon double stars 

 I had myself neglected to make use of the important treatises of M. 

 Yvon Villarceau, which were read at the Institute in the course of the 

 year 1849. (See Connaissance des Temps pour Van 1832, p. 3-128.) 

 I quote here from the table by M. Faye, of the orbital elements of eight 

 double stars, the first four stars, which he considers to be the most cer- 

 tainly determined : 



The problem of the period of revolution of tj Coronae admits of two 

 solutions: of 42-5 and 66-3 years; but the late observations of Otto 

 Struve give the preference to the second. M. Yvon Villarceau finds 

 the semi-major axis, eccentricity, and periods of revolution in years 



yVirginis 3"-446 0-8699 153-787 



^ Cancri 0"-934 0-3662 58-590 



a Centauri 12"-128 07187 78-486 



The occultation oi one fixed s^ar by another, as was presented by f Her* 

 culis, I have called apparent (p. 287). M. Faye shows that it is a con- 

 sequence of the spui'ious diameter of the stars (^Cosmos, vol. iii., p. 66 

 and 170) seen in our telescopes. The parallax c f 1830, Groombridge, 

 which I gave (p. 27) as 0"-226, is found by Schlttter and Wichmann, 

 0"-182, and by Otto Stmve, 0"-034. 



