i^O lujiramait /or txhihitUig Jupiter and his Moons- 



handle will produce one day's motion of every fatcllitc 5 and a continuation of flow regular 

 turn? will produce a pleaGng view of the following plienomena 5 viz. 



1. The fliadows will move in nearly a ftraight line. 



2. Some in a diredl and others in a retrograde direcllon. 



3. The mod diftant will frequently appear the neareft to Jupiter. 



4. Near Jupiter they will move the quickcft^ and floweil near tlieir greateft elongation^ 

 where they become ftationary for a fhort time. 



5. Their greateft elongations will be a little before quadrature, when weft ; and after, 

 when eaft of Jupiter. 



6. Hence it will appear, that the fuperior portion of each orbit is greater than the 

 inferior. 



7. Whether to the eaft or weft of Jupiter, their motions will be dire(fl in the fuperior^ 

 and retrograde in the inferior, parts of their orbits. 



8. When pafTing between Jupiter and the earth (candle) they will tranfit him. 



9. When pafiing the fame line in their fuperior femicircle they will fuffer an occulta- 

 tlon. 



1 0. When pafting through the four concentric circles they will be eclipfed. 



1 1. The mean or apparent times, accordingly as the inftrument may be reftified, of each 

 of thefc phenomena, will be pointed out by the hour-hand, the name of the day by the 

 week-hand, and the day of the month by the month-hand, in each year. 



12. If the candleftick is adjufted frequently for the fun's place and Jupiter's heliocentric 

 longitude, the folar fliadow will appear to alter its fituation to the right and left of Jupi- 

 ter, as he approaches to or recedes from conjun£lion or oppofition. 



13. The reafon will be evident, from the concentric circles, why an immerfion or in-' 

 grefs into Jupiter's fhadow, and a fubfequent emerfion or egrefs out of it, never both hap- 

 pen with the firft and * fecond fatellites ; nor with the third, if Jupiter is within 46° of 

 oppofition to, or conjunftion with, the fun ; nor with the fourth, if that diftance is lefs- 

 than 24°. 



14. It will be llkewife evident why an immerfion only is vlfible of the firft and fecond 

 fatellites from a conjun£tion to an oppofition (fig. 6.), why an occultation and eclipfe may 

 be coincident when at oppofition (fig. 5,), and why an emerfion only is feen from an op» 

 pofitionto a conjun£lion (fig. 4.). 



15. If a proper reclination be given to the fatellitian in this and on the next year, and 

 alfo on every fixth and feventh year hence, the fourth fatellite will neither be eclipfed nor 

 fuffer an occultation. 



id. If a candle be now placed in each foctet of different lengths, as is reprefented in 

 fig. 3. the fhadow of the central one to cover the concentric circles, there will be two rows 

 of (liadows on the fcreen above one another, one of which will reprefent the heliocentric> 



and the other the geocentric, places of the fatellites. 



n 



• An immerfion and fubfequent emerfion may be feen of the fecond fatelllte, provided it be near one of its 

 limits at the fame time that Jupiter is near both his pcrihelioa and quadrature with th« fun ; but this will 

 very rarely happen.— W. P. 



1-7. Hence 



