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XXXVIII. On the Bifappearance of Saturn's Ring in the 

 Year 1803. . Bj Frofejfor J. E. BoDE*. 



1 HE plane of Saturn's ring, as is well known, during 

 the whole of his revolution of thirty years round the fun, re- 

 tains Its parallelifm, and interfefts the plane of the ecliptic 

 in 17 degrees of Pifces and of Virgo at an angle of 31^". 

 The necelfary confequence, therefore, is, that the northern 

 fide of the ring is illuminated for fifteen years by the obliqu* 

 rays of the fim, and then the fouthern for the fame period. 

 It muft alfo happen, that in the above places the plane of the 

 ring paifes twice through the fun in each revolution, at which 

 tinie the edge of the rmg only is illuminated. But the edge 

 or thickn'jfs of the ring being too fmall to admit of its being 

 feen from the earth on account of the great diftance of Sa- 

 turn, the ring becomes invifible. For fifteen years the earth 

 and the fun are on the fame fide of the ring, which is the illu- 

 minated lide, and therefore the ring during that period is 

 always vifible; but a little before, and at that period when 

 the plane of the ring pafles through the fun, or when Sa- 

 turn's heliocentric place is in 17° of x or of m in the afcend- 

 ing cr defcendino nodes of the ring, the earth and the fun 

 mayfirltbeon one fide and then on the other fide of the 

 ring. In the firfl; cafe, as long as its plane does not pafs 

 through the fun it will be vifible from the earth ; but in the 

 other cafe it will be invifible. The earth, therefore, can then 

 pafs feveral times through the plane of the ring, at which 

 time the ring will appear like a right line, or be entirely in- 

 vifible; the confequence of which is, that the ring will be 

 alternately Tifible and invifible. 



This alternation of difappearing and reappearing will be 

 exhibited by the ring in the year 1803. The fun, having 

 illuminated the fouth fide of the ring fince Oftober 1789, 

 will pafs through the plane of it in the month of June 1803, 

 and will illuminate the northern fide, when Saturn pafles 

 heliocentric;:lly the afcending node of his ring; and in the 

 mean time the plane of the ring will pafs three tmies through 

 the earth, which will be firft on the fide illuminated by the 

 fun, and then on the oppofite or darkened fide; in confe- 

 quence of which the ring Icen from the earth will be twice 

 vifible and invifible in the courfe of a few months. 



Thcfe phrenomena will be better comprclunded by infpe^l- 

 ing the annexed figure, which fuppofes the obferver to be 



• From his AftfVKom'if. b Jahr Bucb for 1:03. 



placed 



