37 



specting the cause and consequences of its movements, that 

 leaves out of account the earth's varying degrees of attraction on 

 the different parts of the mass and their effect upon its move- 

 ments, must be erroneous. To me, therefore, it seems unques- 

 tionable that, even if the earth had been originally set a-going 

 by some such oblique impulse as Bernouilli supposes, the rota- 

 tion would have stopt as soon as the whole mass was set in mo* 

 tion, and that it would at all events have become instantly sub- 

 ject to, and been modified and controlled by, the sun's attraction 

 of gravitation, and even stopt at once if it had been in its direc- 

 tion incompatible with the action of the solar centripetal force. 

 In the case supposed, however, its direction would be perfectly 

 consistent with the action of that force, which, so far from hin- 

 dering the rotation, would rather aid it ; but which, at the same 

 time, would be perfectly sufficient of itself to produce that rota- 

 tion, without the primary oblique impulse supposed by Bernou- 

 illi. Suppose the earth to have been travelling straight forward 

 in space at her present mean orbital velocity, but without turn- 

 ing round on her axis, when she came within the influence of 

 the sun's attraction, that power would not merely grasp her cen- 

 tre, but would aff*ect her whole mass with various degrees of 

 force, proportional to their distances from the sun, and those at- 

 tracted most would naturally feel the influence of the attraction 

 in the retardation of their forward movement, while the parts 

 farthest off^ would continue to fly forward with comparative free- 

 dom, and the greater the forward velocity of the mass in its or- 

 bital revolution, the more rapidly would the attracted parts be 

 left behind, to take their turn in the rotation as soon as relieved 

 from the sun's grasp by the lever power of the forward particles 

 acting through the centre of the revolving body. In the rota- 

 tion of a progressing body, as formerly observed, no part of it 

 ever moves or can move backward ; all the particles alike move 

 forward, and only forward, and their retardation is in all cases 

 to be ascribed more probably to friction, or attraction, or other 

 hindrance from without, which are all, in their respective degrees 

 and qualities, more or less sufficient causes, than to any intrinsic 

 power of rotation, from whatever cause originating ; and more 

 especially when such a supposed hidden cause is not indispensably 

 essential to the production of the visible effect Bernouilli's hy- 

 pothesis, therefore, is clearly at variance with Newton's rule of 

 philosophizing, which requires us never to assume more causes 

 of natural events than are true, and sufficient to account for the 

 phenomena. It cannot be called true so long as it is improbable, 

 and it cannot be called sufficient^ inasmuch as it ascribes two 

 kinds of movement in contrary directions in the same body, to 

 the same cause, namely, the action of the centrifugal power, and 



