

66 



point of its surface to this radius." So this great mechani- 

 cian seems to have believed it possible for a radius -vector that 

 A'emains always positively attached to the same point of a globe, to 

 describe a circle all round the globe's circumference, without ever 

 leaving or stirring from the point to which it is so attached. For 

 '' at the same time that the radius traces the circumference," the 

 globe itself, moving apparently in the same direction, " brings al- 

 ways very nearly the same point of its surface to this radius." This 

 means in plain English, that the radius never describes any cir- 

 cle at all round the moon's circumference, because the same point 

 of circumference remains always attached to it, and will not al- 

 low it to set out on its circumferential journey, which in conse- 

 quence is never made. 



Far be it from me to think of disparaging the fair fame of 

 Laplace ; but, in this case, he seems to have been very greatly 

 mistaken. Whether, however, the mistake lie with him or with 

 me, and, whether or not I have made out the point 1 have been 

 contending for, I shall now leave it to the public to determine, 

 and the determination may be made very easily, for the demon- 

 stration is grounded on the following simple questions: 1. Is 

 it possible for a ball, fixed on the point of a rod or stick, to turn 

 round on its axis while it remains so fixed ? 2. Is it possible for 

 a wheel moving along a rail to turn round on its own axis, and 

 at the same time keep the same point of its circmuference con- 

 tinually in contact with the rail ? 3. Is it possible for a rod or 

 stick to turn round on both of its two ends at once ? or to turn 

 round on its middle while one end is held fast ? Is it possible for 

 a cord, attached by one end to the centre of a circle, and having 

 its other end attached to the surface of a globe or wheel, either 

 revolving round the circle, or remaining stationary at one point, 

 to be drawn round about the circumference of the globe or wheel, 

 unless that body turn round on its axis ? To these questions I 

 answer No ; but the astronomical doctrine I have been combat- 

 ing requires all the answers to be in the affirmative. Which of 

 us is right ? 



Edinburgh, ISth March 1847. 



J. L. 



CORRIGBNDUM. 



P. 11, line 34, after degree, insert — " of its circumference, while moving through 

 one degree." 



