o^ 



2 On the D'tfappearance of the Ring of Saturn, 



The {late of the atmofphere alfo, and the different power of 

 the telefcopes and of the eyes of the obfervers, may occafion 

 foine variation. The difappcarance and reappearance of the 

 ring, which are occafioned by the earth palling through its 

 plane, can be belter and more conveniently obferved than 

 thofe which take place in confequence of the pallage of the 

 fun through that plane, becaufe the earth, on account of its 

 quicker motion, partes fooner through the plane of the ring 

 than the fun. 



As the fix fir.H; fatellitcs of Jupiter move in the fame p]an6 

 with the ringj when the ring difappears, or becomes like a 

 luminous line, thefe (iitellites mu(t appear on both fides ot Sa- 

 turn in a right line, and can then be more readily dilcovered 

 and diilinguilhcd from fixed ftars. 



XXXIX. On the Difappearance of the Ring of Saturn. By 

 Van Beeck Calkoen, Profeffor of AJlronomj at Ley- 

 den *. 



J. HE plane of Saturn's ring, according to aftronomlcal 

 obfervations, has always a direAion parallel to itfelf, fo 

 that it interfefts the ecliptic in 17° 18' of iiR and X, at an 

 angle of 314:°, and the orbit of Saturn at 20" 42,^ of i>k and 

 X . Now, if Saturn as feen from the fun be in longitude 

 20° 42' of X, the plane of the ring will pafs through the 

 centre of the fun ; by which the edge of the ring being illu- 

 minated, while the northern and fouthern furface receive no 

 light, it muft become invifible, and can be feen only by the 

 jTioft powerful telefcopes as a fine luminous line. On the 

 i^th of June next Saturn will be in this fituation ; and as this 

 planet employs about thirty years in its revolution round the 

 fun, (his phaenomenon takes place only once in 15 years. 

 Other phasnomena, however, in confequence of which the 

 ring before the I5lh of June will allernaiely difappear and 

 reappear, are conneiiled with this ilate of the planet. Thefe 

 phienomena arife from the different pofitions of the earth, 

 which in the courfe of its revolution is at one time above 

 and at another below the plane of the ring; fo that from 

 the ill of November 1802 to Oftober 1803 the ring will 

 be twice invifible and twice vifible; firft the fouthern and 

 then the northern, then the fouthern and afterwards the 

 norlhorn furface will be alternately feen from the earth 

 VKithin the courfe of ten months. For determining and cal- 

 culating thefe phsenomena with more accuracy, Lambert in- 



" From Algcmeene Konjl cii Letter. Bode, No. 13, for i£o3. 



vented 



