R74 Geographical Position of the 
IIl.—Ectirsts oF JupITeR’s SATELLITES. 
as Mean Time Mean Time at | Resulting 
No DAS Ee eo Emersion at Greenwich by | Longitude 
E a or Van Diemen's the Nautical East of 
1852, = & | Immersion, Land. Almanac. Greenwich. 
D. H. M.S. D. H. M.S, H. M. Ss. 
1 May 15th} II Emersion 15: 12° 33: 52:4 | 15° 2° 44: 95-4 | 9 49° 27- 
2 May 26th i Emersion 26° 14: 17: 23-7 | 26° 4° 97° 49°8 | 9 49- 33°9 
3 May 28th I Emersion | 28 8 46: 00- | 27: 22° 56- 26° 9: 49° 34° 
4 June 4th I Emersion 4° 10: 40: 23-3 | 4: 00° 50° 49°5 | 9° 49° 33°8 
5 June llth I Emersion | 11: 12° 34: 46:6 | 11: 2° 45: 17°7 | 9° 49° 28°9 
6 June 13th I Emersion 13" 7: 03: 29°2 | 12° 21° 13° 53°7 | 9° 49° 35°5 
7 June 16th | II Emersion | 16: 12° 15: 50-7 | 16° 2° 26: 09-2 | 9° 49> 41°5 
8 June 20th I }|- Emersion | 20° 8: 57- 54:1 | 19° 23° 8: 26:9 | 9: 49: 27:2 
9 June 27th i Emersion | 27: 10- 52: 24-8 | 27° > 3: 3:8} 9: 49: 21° 
10 July 4th II Emersion 4 6-47: 13:4 | 3- 20° 57- 31:8 | 9° 49: 41°6 
Whence we have— H. M. & 
By seven emersions of the Ist Satellite... 9° 49° 30°6 
By three ditto 2nd Satellite... 9° 49° 86°7 
Mean .... 9° 49° 38°65 
With reference to observations upon the eclipses of 
Jupiter's Satellites, the Nautical Almanac says :—“ Inde- 
“pendent of defects in the Tables, there are difficulties 
“ attending the observation of these phenomena which 
“unfit them for accurate determinations of longitude. 
‘ Tifferent telescopes give different results, and care should 
“be taken to have recourse to those corresponding obser- 
“‘ vations which have been made under circumstances the 
“‘ most similar, and particularly with telescopes of the same 
“ quality and power.” 
I have employed the same telescope and an eye-piece of 
the same power throughout, and although bowing of course 
to the indisputable opinion of the Nautical Almanac upon 
such points, I still think that, when a sufficient number of 
these observations are carefully made, with a due atten- 
tion to the clearness of the atmosphere and steadiness of 
