56 



r, &c., in succession, turning the mass round on its axis to the 

 extent of one-eighth part of its circumference during its progress 

 along each octant of the orbit, while B and its successors were 

 simultaneously falling back to the same extent, in the opposite 

 direction. Whatever be the size of the revolving body, and its 

 proportion to the circumference of its orbit, the process and the 

 result will be, in all cases, precisely the same. It may be scarcely 

 necessary to add, that what takes place with the octant points, 

 happens equally with every one of the body's intervening points, 

 all of which, at every instant of progression, take precisely the 

 same course as the octant points specially referred to. At every 

 instant each of them takes a step forward, while the axis is turning 

 in the opposite direction, without carrying them back to their 

 original places, relatively to itself. 



This great mistake of Galileo's, later astronomers and me- 

 chanicians have fully adopted ; and, believing the moon to be 

 fairly represented by the water in the basin, and that the water 

 so placed does not rotate, they have very naturally indeed, but 

 too hastily, jumped with him to the conclusion, that^ to enable 

 the moon to '-'bring the same point of her circumference continu- 

 ally back to the radius," she must have a power to rotate, and 

 does rotate, in a direction *' contrary to that of her revolution." 

 " Contrary," the direction of this alleged rotation must be called ^ 

 for unless it were " contrary" it could not be true ; and yet, "con- 

 trary," as it is called, it is not the less precisely in the same di- 

 rection as the line of revolution ; for it is from west to east, and 

 the revolution is so too. Galileo might have taught them bet- 

 ter, for he rightly says, that the water's visible rotation in the 

 basin is contrary to the direction of the basin's orbital revolu- 

 tion ; and if that be correct, as it unquestionably is, then must 

 the moon's alleged rotation in the opposite direction, from west 

 to east, be not contrary to, but in the same direction as, the re- 

 volution ; and, being in the same direction, its inevitable I'esult, 

 if it existed, would be the presentation of every part of her cir- 

 cumference in succession to the earth. As a wheel, moving 

 along a rail, and rolling forward in the same direction, carries 

 every part of its circumference in succession to the rail, and past 

 a straight line drawn across it through its axle perpendicular to 

 the rail, so would the moon, revolving as she does, and rotating, 

 as alleged, in precisely the same way as the wheel, carry every 

 part of her circumference past her radius- vector, and all round 

 about. But, besides adopting Galileo's error, some of them have 

 made a far greater mistake of their own, for they have supposed, 

 what he did not, that there is a third ])ossible way of an observ- 

 er's seeing the whole circumference of a globe, namely, by hav- 

 ing it carried round about him without turning round on its own 



