R O N o M y.

A s T

a^p, s ’ at the Distance of 25A Semidi->

(CXXXVI),

Saturn

t'h ) 1. Galileo first discovered the Satel-

Hfjr rn os Jupiter , in the Year 1610 ; and call’dtjie p a * Sidera, or Mpdicean Stars, in Honour ofj' e ce Ca j! y °s the Medici, his Patrons. The famous^scribg l ^ ereus Nuncius , in which he particularlyv discovery of these Stars, he dedicated totru n n . S ^ ed ices II. the fourth Great Duke of He-

,'anc e Orbits of Jupiter’s Moons lie nearly in thePotion i ^oliptic, which is the Reason why their5 ? it re;i j. S Apparently in a right Line, and not circular,A th e v? * s > To understand this, let S be the Sun,' s ^rbit^A 1 ' n ' ts Orbit I H, I the Planet Jupiter in. his !\ ; j /*• I B, and in the Centre of the four Orbits

^ s < 0ons - , _ : _ -

the e earI y pass through the Eye, the real Motion

Gtelll** * -.u- t>_ • 1 ... . *11 i. _ _^i_.

Then, because the Plane of those Or-

fre jy ^Gtellitg in the Periphery will be apparently intQ the a r meter of the Orbit, which is at Right Angles}her % L >ne joining the Centre of the Earth and Ju-,

sll PPosing the Earth at R,.if D C be drawnMotion t ? c Ce ntre of Jupiter perpendicular to R I, tirei n \l nf each Moon and their Places will appear tper j P a t Line. Thus if the exterior Moon be at L

V Cei Wi11 appear to be at I, either upon or behindK it of Jupiter ; if the Moon move from E to

a Ppear to have moved from I to L ; an^ves from K to C, it will appear to moveC to wA° C. Again, while the Satellite moves romA goes f lt: ' V '-H appear to move from C to L ; and as*o I ^oin thence to F, it apparently moves from L

V S a J, hu s also on the other Side the Orbit, whilewo t ; ,lte describes the Quadrant F D, its apparentVi n VVl . 11 be fr om I to D ; and then from D to I. 4. \A- S , **■ c °mes from D to E.

iUp De lence 5 since this is the Cafe of each Satellite,ars rhat while each Satellite describes the remote

Half