( 313 ) 



If we assume 9°42' = 38^48» East of Greenwich for the longitude 

 of Hannover, this is = 6'» 16^ 12^ M. T. of Greenwich, at least sup- 

 posing that at that time it was already usual to give the observations 

 expressed in mean time. 



In Nature, XVII (Nov. 1877-April 1878) p. 149 (not J 48) we fmd 

 in "Our Astronomical Column'": 



"Jupiter's S.^tellites. — Amongst the recorded phenomena connected 

 with the motions of the satellites of Jupiter are several notices of 

 observed occultations of one satellite by another, and of small stars 

 by one or other of the satellites. ^) The following cases may be men- 

 tioned: — On the night of November 1, 1693, Christoph Arnoldt, of 

 Sommerfeld, near Leipzig, observed an occultation of the second satellite 

 by the third at lOb 47m apparent time. On October 30, 1822, Luthmer, 

 of Hannover, witnessed an occultation of the fourth sateUite by the 

 third at 6^ oSm mean time. 



It thus appears that the editor of Nature also took it for granted 

 that the statement must be understood to have been made in mean time. 



(4) I did not succeed in finding the account of this observation 

 of Stanley Williams in any of tlie journals accessible to me, and 

 therefore applied to the author, who lives at Hove near Brighton, 

 for particulars about the place of its publication. 



He kindly replied on the 7^'^ instant, that the details of liis obser- 

 vation of 27 March 1885 were published both in the 41''' volume 

 of the ''English Mechanic" and in the volume for 1885 of the German 

 Journal ''Sirius". 



He had moreover the courtesy of commuiiicatiug to me the original 

 account of the observation in question. From this account the 

 following passages may be quoted : 



Occultation of sateUite I by satellite III. 

 1885 March 27, ... . 2'/, incii refractor. Power 102. 



11''55"^ (Greenwich mean time). They are now only J?^.9^ free from 

 contact. ^1 , like an elongated star witii little more tlian a 



black line between the components. 



12'00'" to 12''04m. After steady gazing I cannot see any certain 

 separation between the satellites, and thci-efore with this instrument 

 and power first contact must have occurred about 12''02'^. Definition 

 is very bad, however, and in a larger telescope there probably might 

 still be a small separation between the limbs. 



1) It is to be regretted that these "several notices of observed occultations of 

 one satellite by another" are not more fully quoted. 



21 



Proceedings Royal Acad. Amsterdam. Vol. IX. 



