Prof. Airifs Researches into the Mass of Jupiter. 383 



satellites at anv time, and tables for facilitating their application to 

 the first. And he concludes with remarking, that of other satellites 

 than these two he has no evidence ; but if any exist, he hopes soon to 

 procure a sight of them. Neither has he ever seen any appearance 

 about the planet which gives ground for the least suspicion of a ring. 



II. Continuation of Researches into the Mass of Jupiter, by Ob- 

 servations of the Elongations of the Fourth Satellite. By Professor 

 Airy*. 



The results of this paper are founded on six sets of measures, made 

 in the same manner as the last, and with the same instrument, before 

 the opposition of Jupiter. The unfavourable state of the weather 

 after the opposition prevented any more being made. By observation 

 of S Ursa Minoris in different positions of the instrument, the errors 

 of the line of collimation, and the declination and polar axes, were 

 found to be very small, as was also the rate of the clock. In every 

 instance, twelve transits over three wires were obtained, both of the 

 planet and satellite. 



The mode of calculation in this paper differs from that in the pre- 

 ceding, in a correction applied to the observed difference of right as- 

 cension for refraction ; in the addition of Ot'0073 to the mean longi- 

 tude of the satellite in finding the Jovicentric right ascension, for 

 reasons mentioned in the Memoirs of the Society, vol. vi. p. 98 ; and 

 in subtracting S "0050, or Os-0054, for the equation of the equinoxes. 



The following are the individual results : — 



The constant difference between preceding and following observa- 

 tions of the satellite does not exist in the above series ; and Professor 

 Airy states that he is unable to determine whether this arises from the 

 smallness of the number in the series, or frpm some alteration in his 

 method of observing. 



Considering all of the preceding as entitled to equal credit, the 

 log. mass of the sum of the planet and satellite is 69797157, 

 or (as in the former paper) the log. mass of the Jovial system is 



6-9797717; the corresponding number is ,-., ^ Q . that found in 

 r ° 104/-68 



the preceding paper being 



1 

 1018-70' 



On this difference, Professor 



Airy observes : " If this proceed from an error in the inclination of 



* For accounts of Profewor Airy'* former researches on this subject, stu 

 Loml. and Edlnb. Phil. Mag., vol. ii. p. .'{14, and vol. iii. p. 238. 



