54 



possesses not only the power, but also, what the moon has 

 not, \\\Q freedom to rotate in the opposite direction ; and using its 

 freedom, away it flies round and round about continually, the 

 particles of its circumference, and generally of its whole mass, 

 changing their place-relation to the axis and to the radius- vector, 

 and to the orbit and its centre, at every instant of progression. 

 Even when water is used by itself in the experiment, a portion 

 of its particles adheres to the sides of the basin, and remains be- 

 hind, while the rest of the mass moves round about. According 

 to the astronomic doctrine, the reason of this is, that the par- 

 ticles so adhering, and lying still with the basin, rotate or turn 

 round on the water's axis, in that direction, while the rest of the 

 water stands still. *' Credat Judceus Apella ; nan ego." 



Galileo says that a body suspended freely in space naturally 

 without any moving cause acquires a rotation round its own cen- 

 tre. But a moving cause there must be, and the cause of the 

 water's rotation is this. The different parts of the water's mass 

 have different orbits of revolutions, and, if they were to keep to 

 these orbits, there could be no rotation, and the same point would 

 be constantly presented to the centre of the orbit ; but, as they 

 are all carried round their orbits with precisely the same degree 

 of velocity, by virtue of continued impulse of the same single 

 moving power, that point of the circumference that is inside of the 

 orbit, and nearest the experimenter, can find space for itsjourney 

 only by going outside of its orbit, and consequently turning it- 

 self and the whole mass round on its axis to the same extent, 

 while the outer portion of the circumference as necessarily falls 

 within its proper orbit, leaving the centre alone to follow the 

 mean orbit of the mass. In this way the three points, namely, 

 the outermost point of circumference, the innermost point, and 

 the centre, travel precisely the same distance, in the same time, 

 with the same velocity ; thereby causing a rotation of the body 

 round its own axis ; or, what is the same thing, preserving the 

 perpendicularity and parallelism of its particles, while the axis is 

 continually changing its place. This may be further illustrated 

 in the following manner. 



A body revolving in an orbit has a certain definite breadth, 

 whereby it happens that its outside, or the outer part of its cir- 

 cumference is farther distant than the inside or inner part of the 

 circumference from the centre of the orbit. Consequently, in 

 travelling round the orbit these outer parts have a longer space 

 to run through, which they can only accomplish by means of a 

 greater degree of velocity. But, if it were required that the outer 

 and inner points of circumference, A and B should proceed 

 with neither more nor less than precisely the same degree of ve- 

 locity as the centre C, and yet complete their revolution in pre- 



