EADIATIONS OF THE STABS. 65 



than Jupiter himself; occasionally, however, as shown Dy 

 recent observations, they appear like gray spots on the pifanet. 

 The rays or tails, which to our eyes appear to radiate frctf 

 the planets and fixed stars, and which were used, since the 

 earliest ages of mankind, and especially amongst the Egyptians, 



to me, "but I have found, contrary to my expectations, 

 that they are not of the 5th magnitude, but, at most, only 

 of the 6th or even of the 7th magnitude. The 3rd and brightest 

 satellite alone appeared nearly equal in brightness to a neigh- 

 bouring star of the 6th magnitude, which I could scarcely 

 recognize with the naked eye, even at some distance from 

 Jupiter; so that, considered in reference to the bright- 

 ness of Jupiter, this satellite would probably be of the 

 oth or 6th magnitude if it were isolated from the planet. 

 The 4th satellite was at its greatest elongation, but yet I 

 could not estimate it at more than the 7th magnitude. The 

 rays of Jupiter would not prevent this satellite from being 

 seen if it were itself brighter. From a comparison of Alde- 

 baran with the neighbouring star 6 Tauri, which is easily 

 recognized as a double star (at a distance of 5 minutes), 

 I should estimate the radiation of Jupiter at five or six minutes, 

 at the least, for ordinary vision." These estimates cor- 

 respond with those of Arago, who is even of opinion that this 

 false radiation may amount in the case of some persons to double 

 this quantity. The mean distances of the four satellites from 

 tb' centre of the main planet are undoubtedly I' 51". 2' 57", 4' '42", 

 and 8' 16". " Si nous supposons que 1' image de Jupiter, dans 

 certains yeux exceptionnels, s'epanouisse seulement par des 

 rayons d'une ou deux minutes d'anaplitude, il ne semblera pas 

 impossible que les satellites soient de terns en terns aper9us, sans 

 avoir besoin de recourir a 1'artifice de 1'amplification. Pour 

 verifier cette conjecture, j'ai fait construire une petite lunette 

 dans laquelle 1'objectif et 1'oculaire ont a peu pres le meme foyer, 

 et qui des lors ne grossit point. Cette lunette ne detruit pas 

 erttierement les rayons divergents, mais elle en reduit consider- 

 able ment la longueur. Cela a suffi pour qu'un satellite con- 

 venablement ecarte de la planete, soit devenu visible. Le fait a 

 ete constate par tous les jeunes astronomes de 1'Observatoire." 

 " If we suppose that the image of Jupiter appears to the eyes 



VOL. III. ? 



