1835.]: 



On the velocity of light. 



2^3 



real revolution we have the daily motion of Jupiter in his 

 orbit 4m. 59.26s.* consequently in a Synodic revolution 

 the satellite performs 360d. 4m. 59s. 26 and by the rule 

 of thn-e we find that as 360d. 4m. 59s. 26 : Id. I8h. 28m. 

 3.5s. 77 : :"360d. : the time of a sidereal revolution or Id, 

 I8h. 27m. 33s. 32; or it appears that when Jupiter moves 

 with his mean velocity or at the rate of 4m. 59s. 26 in a 

 day, the satellite after quitting the shadov/ of Jupiter has 

 to move through a complete revolution and for Im. 2s. 45 

 more^ until it will again leave the shadow — were the mo= 

 tion of Jupiter in his orbit double of this amount the sa- 

 tellite after completing one revolution would have to tra,- 

 vel for 2m. 4s. 90 until it would arrive at the edge of the 

 shadow &c. — thus much being premised we will now 

 consult observation ; for this purpose some observations 

 made at the Madras Observatory are available as fol- 

 lows :— 



h. m. s. 



1834 October 16 Immersion of 1st Sat. 16'21-4L 



1835 March,. 30 Emersion 9- 7'24". 



— April..,. 15 7-28- K 



in selecting the above out of a great many, care wa« 



taken that the circumstances with regard, to distance 

 from the Earth should be as near to the extremes as 

 p<?ssible, thus at the first observation the distance 

 of Jupiter from the earth was, miles. . . .387/700,000 



at the second, .520,500,000 



. third . . ..... « 54o.,000,00a- 



the above, however, are not the best observai ions adapted 

 to our purpose, inasmuch as, the first is an oliscrviition of 

 the Immersion of the satellite into the shiulow of Jupi- 

 ter or the beginning of the eclipsCj whereas the second 

 and third are the observation of the E/ner-sio?/ or the end 

 of the eclipse, hence it becomes necessary to reduce the 



* Jupiter performs his Sidereal revolution in -lo-'Ji uH) tf 11 luairs which, 



gives 4' 59" 2B for his daily motion. 



