224 ^" ^^^ Di/apptarance ef the Ring of Saturn. 



non be viewed, the appearance will be the fame. The ring 

 till the 15th of June will continually become fnialler, and on 

 that day will be converted into an almoft imperceptible line 

 of liiiht. The difappearance then of Saturn's ring on the 

 15th of June, or rather its decreafe till that period and its 

 fubiequent iiicreafe, arifes alone from the relative pofition of 

 Saturn and the inn. As to the other caufcs of difappearance, 

 which are the confequence of Saturn's pofition in regard to 

 the earth, we muft tirft keep in view the flow motion of 

 Saturn compared to that of the earth, as this planet advances 

 fcarcely 2^ in the time that the earth performs its revolu- 

 tion around the fun. On the 15th of June, at which time 

 Saturn will be in 20' of X, and the plane of the ring will 

 pafs through the fan, the interfeftion of that plane with the 

 ecliptic, or the line ZS in the figure, pafl'es through the mid- 

 dle of the earth's orbit. During the laft fifteen years, while 

 Saturn advanced from T to nj, this liue of the plane of the 

 ring was without, and above the earth's orbit, and during 

 that period the foulhern and luminous part of the ring was 

 ahvavs vifible; but about the middle of December 1802 this 

 litie approached the earth's orbit, and on the 13th of De- 

 cember pafled through it exactly in the point where the earth 

 then was. The earth being then in the plane of the ring, 

 the thicknefs of the ring only could be vifible to us ; and 

 thus, for the firfl time in fifteen years, difappeared on the 13th 

 of December 1802, On the other hand, as the earth moved 

 ftraiffht towards Saturn, or parallel with that line, while Saturn 

 advanced, it was necelfary that the fouthern furface of the 

 ring hitherto vifible fliould become invifible, and the north- 

 ern, which was not illuminated, being turned towards the 

 earth, the whole ring would become invifible. But as the 

 earth proceeded in its orbit it would foon reach the line of 

 the phiiie, and on the 7 th of January 1803 would again pafs 

 throuah it. At that period, the fouthern furface of the ring 

 being illuminated by the fun would again be vifible from the 

 eartii^; but as the earth on tlie 21ft of June muft in its revo- 

 lution be ajrain on the other iide, Saturn in his courfe fiiUing 

 in with the earth in the plane of the interfe6lion of the ring 

 and the ecliptic, will again pafs through it on the 18th oT 

 Aneuft, at which time the ring will appear once more as a 

 fine" ft ripe of light. After that day the northern furface of 

 the ring will be vifible from the earth, and, as the line of the 

 plane will then be without the earth's orbit, will, during the 

 next fifteen years, remain always vifible. 



From the 7th January to the 21 ft of June, the fouthern 

 furface of the ring being illuminated, the ring will be vifible; 



but 



