50 



FERGUSON'S LECTURES. 



The 

 earth's 

 motion 

 demon- 

 strated. 



LECT. f hangs over the center of the 

 1 t, as the ball g will be kept 

 towards the moon by the heaviest 

 weight p, (see page 47.) and the 

 ball e, on account of its greater 

 centrifugal force, and the lesser 

 weight r, will fly oft* as far to 

 the other side, (as in this engrav- 

 ing.) And so, whilst the machine is kept turning, the 

 balls e and g will hang over the ends of the ellipses 

 Ifk. So that the centrifugal force of the ball e will ex- 

 ceed the moon's attraction just as much as her attrac- 

 tion exceeds the centrifugal foree of the ball g, whilst 

 her attraction just balances the centrifugal force of the 

 ball f, and makes it keep in its circle. And hence it 

 is evident, that the tides must rise to equal heights at 

 the same time on opposite sides of the earth. This 

 Experiment, to the best of my knowledge, is entirely 

 new. 



From the principles thus established, it is evident that 

 the earth moves round the sun, and not the sun round 

 the earth : for the centrifugal law will never allow a 

 great body to move round a small one in any orbit what- 

 ever ; especially when we find that if a small body moves 

 round a great one, the great one must also move round 

 the common center of gravity between the two. And 

 it is well known that the quantity of matter in the sun 

 : 227,000 times as great as the quantity of matter in the 

 earth. Now, as the sun's distance from the earth is at 

 least 81,000,000 of miles, if we divide that distance by 

 227,000, we shall have only 357 for the number of miles 

 that the center of gravity between the sun and earth is 

 distant from the sun's center. And as the sun's semi- 

 diameter is \ of a degree, which, at so great a distance 

 as that of the sun, must be no less than 381,500 miles, 

 if this be divided by 357, the quotient will be 1068?, 



