An Astronomical Machine, the Tellurium. 341 



plate d by means of its own gravity, and slides along this plate 

 as c turns round, the wire alternately rising and falling in its 

 socket ; consequently the orbit in which the moon V moves must 

 always be parallel to the plate d, and form an angle of 5^ degrees 

 with the plane of the ecliptic. The index e, which points to the 

 moon's apogee, is fixed upon the socket of the wheel H. The 

 axis g carries four wheels A, E, G, and I, which all turn as one 

 wheel. Next to the wheel A is placed the pinion of a wheel B, 

 •whose teeth act upon the teeth of a small wheel ]), which trans- 

 mits motion to the pinion C. The teeth of the wheel E act 

 upon the teeth of the wheel O, whose axis also carries a wheel 

 P, which gives motion to the wheel D. The teeth of the wheel 

 G act upon the teeth of the wheel F ; and lastly, motion is trans- 

 mitted from the wheel I to the wheel H by means of an inter- 

 vening wheel r. 



When the winch n is turned by a steady hand, the leaves of 

 the pinion N act upon the teeth of the large circular wheel M. 

 and turn it and the elliptical L on their common axis with an 

 equable motion. The teeth of L at the same time act upon those 

 of the wheel K. As K turns, the arms h and i both move in the 

 same direction and carry the movable frame 5 6 7 8 parallel to 

 itself, over and over the top of the large stationary frame 12 3 4. 

 The earth U is carried along with the moving frame, and has the 

 parallelism of its axis also rigidly preserved. As the ends of the 

 axes/ and g slide round in the elliptical grooves, in the board 1, 

 it is apparent that the orbit described by the earth U, must be an 

 ellipsis of the same size and eccentricity as either of these grooves. 

 When the earth is in its perihelion, as represented in the draw- 

 ing (Plate V,) that part of the circumference of the elliptical 

 wheel L, which is farthest from its axis and has the greatest ve- 

 locity,_ is applied to a part of the circumference of K which is 

 nearest to the axis of the latter wheel, consequently the earth 

 must have its quickest motion. When the earth comes to its 

 aphelion, these elliptical wheels have a reverse position with re- 

 spect to each other, which gives the earth its slowest motion. 

 These elliptical wheels working together in this manner, give the 

 earth U the same unequable motion in its orbit, that the real' 

 earth has in nature. 



The wheels A, E, G, and I, all make one complete turn on 

 their common axis g durmg an entire revolution of the earth 



