MADE AT LANCASTER. 117 



23d. The ring of Saturn invisible, though I looked for it 

 with both telescopes* during the twilight, and half an hour 

 after. By the theory of Mr. Sejour, the disappearance of the * 

 ring ought to have taken place on the ^Sfhf; and, perhaps, 

 with better telescopes, that would have been the case; for 

 much depends upon the goodness of those instruments, and 

 the state of the atmosphere at the time of making the obser- 

 vations. — With Mr. HerscheFs large telescope there is no real 

 disappearance. It is likewise possible, that tire difference be- 

 tween the disappearance as resulting from the theory, and ob- 

 servation, may, in part, be owing to a small retrogade motion 

 in the nodes of the ring. 



Sept. l 23d. The moon occulted a star at 8 h 43' 51" mean 

 time, or S h 51' 28" apparent time. The star is in the con- 

 stellation of Sagittarius ( $ ), and supposed to be the one num- 

 bered 71 '2 in Mayer's catalogue; — it is of the 6th magnitude: 

 the star appeared to remain well defined 4- or 5 seconds on the 

 moon's limb, but the disappearance was instantaneous. 



I shall now, after a preliminary observation, proceed to 

 state the results of the foregoing observations on the eclipses 

 of Jupiter's satellites, as deduced both from Mr. Delambre's 

 tables, and the British nautical almanac. — As a standard of 

 comparison I shall consider the correct longitude of Lancas- 

 ter to be 5 h 5' 4" west, from the observatory at Greenwich; 

 and which I am persuaded will not be found many seconds 

 erroneous]:. 



L,ong. by Delambre's tables. Long, by the naut. almanac. 



h I II h I II 



1803, March 1st. Immer. 1st sat. 5 5 21 5 5 58 



too great 17 too great 54 



11th. Immer. 2d sat. 5443 5 6 28 



too small 21 too great • . . 1 24 



* One of them a Reflector with a magnifying power of 300. 



•(• Essai sur les phenomenes relatifs aux disparitions periodiques de V anneau de Saturn. Par 

 M. Dionh Du Sejour. Pages 165 & 166. 



J Note, Agreeably to the tables of Mr. Delambre, the longitude of Lancaster, by a mean of 

 the five observations on the eclipses of the 1st satellite of Jupiter, appears to be 5h 5' 10" west 

 from Greenwich ; which exceeds the assumed standard 6 ' : — And if a mean of all the determina- 

 tions, agreeably to the same tables, be taken collectively, the longitude will be 5h 5' 4" west from 

 Greenwich, which agrees exactly with the assumed standard. 



