88 DESCRIPTION of the 



fine effect, efpecially as the fupporting wires of the pla- 

 nets will be dark and fo fmall as to render them almoft 

 invifible, the frame being fufpended from the ceiling. 

 Their latitude may readily be afcertained by a line drawn 

 from the centre of the fua through that of the planets 

 place to the hoop / / encompaffing the whole, marked 

 with eight degrees on each fide of the ecliptic. The 

 elliptic orbits and inclined planes are obtained by the me- 

 thod fliewn in fig. 2. viz. 



a a is zn elliptic plane fiiftened to the lower end of each 

 fixed cannon, having its excentriclty calculated to that 

 of the planet which is to be affected by it. ^ /5 is the 

 arm attached to the moveable cannon. r l- is a Aider 

 moving on the arm ^ ^ by four little fridlion rollers, d 

 is a fridion wheel on the under fide of c turning on a 

 pin which is fafiened firm in c and moves, with it, through 

 a groove m b l> which wheel running againfl: the edge 

 ot the ellipfis a a, forces c c out, which is again drawn 

 in by the fpring c, thus caufing the planet to revolve 

 in an elliptic orbit, as it is carried round by the arm b b^ 

 the moveable cannon, and wheel work. 



For the inclined plane, ^ is a wheel turning on a pin 

 fafiened into c c, and carried round on it by a projecting 

 arm of b'*. On one fide of this wheel is a fmall pin, 

 whofe fituation and difiance from the centre is to be de- 

 termined by the place of the planet's nodes and the in- 

 clination of its plane to that of the ecliptic : to this 

 pin is fafiened a fmall waxed filk cord which pafiing over 

 the pulley h fuppoits the planet by a fine hair wire, as 

 before dcicribed and draws it up and lowers it down in 

 Its orbit accordiiig to its angle of inclination to the plane 

 of the ecliptic. The planets fliould be made of poliihed 

 metal to give them weight and brilliancy, or of hnall 



glafs 



* The circunifcrcnce of the wheel mud be commenfuratc ■vviih the dif- 

 taiice c c moves out. 



