15* 



EJLIPSES OF THE SATELLITES OF JUPITER. 



Clock. 



Circumstances 

 noted. 



Longitude of 

 Madras. 



80 ; having been constructed more immediately for this pur- 

 pose, for which they were exceedingly well calculated in all 

 respects. 



An astronomical clock, with gridiron pendulum, and dead 

 beat, regulated by transits of the sun and stars, was used 

 for the time; which was deduced from the transit of the sun 

 nearest the eclipse, and verified by the one immediately pre- 

 ceding or following. 



The circumstances under which the eclipses were ob- 

 served are noted; from these may be inferred, how far the 

 results are to be depended upon : those observed with th« 

 " air clear and the planet high 1 ' are the most satisfactory 

 and valuable, nothing to the contrary being afterward ex- 

 pressed. 



The longitude of the place, by numerous observations of 

 various descriptions, is oh :21 : 14", or 80°: 18': 30' enst of 

 Greenwich: by comparing this with the numbers in the 

 la^t column, the difference of the tables will be obtained. 



The greater number of these eclipses were not visible at 

 Greenwich, but have been found very useful, when corres- 

 pondent observations have been taken in India. 



Persons not much in the habit of observing these eclipses, 

 but desirous of obtaining as much correct information from 

 their observations as possible, may find the following gene- 

 ral remarks of use. 

 Correspondent A correct difference of longitude, it would appear, is not 

 observations to be expected, by comparing the time of observation with 

 that in the tables ; it therefore becomes necessary to have a 

 correspondent observation to compare with, or some satis- 

 factory observations taken under a known meridian, about 

 the time; from which the crrours of the tables may be 

 found. Correspondent observations should, however, be 

 obtained if possible : but it must not be supposed, that even 

 these will give a correct difference of longitude, unless ob- 

 served at both places, under the like favourable circumstan- 

 ces, and with telescopes of the same powers. 



The air being clear ; the planet so high as to be out of 

 the thick atmosphere, and to make the position easy; the 

 telescope sheltered from the wind, and steady; neither moon- 

 light nor twilightj and the satellite not near the body of the 



planet ; 



General re 

 marks. 



necessary. 



Most favour- 

 able circum- 

 stances. 



