Mr. A, Day on the Rotation of the Pendulum. 21 



reasons why it should be adopted implicitly, without one to be 

 urged on behalf of the ancient hypothesis which makes the earth 

 stand still. We have heard indeed of incredulity on this point, 

 but it must be confined to those who, with their systems of phi- 

 losophy or theology, stand as still as the earth on their theory ; 

 and to offer a serious refutation would be loss of time, without 

 the hope of bettering the state of their convictions. Notwith- 

 standing however that the mass of men are fully agreed on this 

 question, and that the great conspiracy of arguments tends to 

 render the conclusion in the highest degree probable, and to the 

 philosopher certain, it cannot be denied that a diurnal rotation 

 of the heavens would produce effects such as those ordinarily 

 observed, and that the reasons which lie against it are not those 

 which can be easily understood by persons unskilled in physical 

 demonstration. We are glad then of a new fact, which, though 

 it does not really make the rotation of the earth more a sensible 

 phsenomenon than before, shows that a relative motion exists 

 between the earth and other independent planes, in which the 

 same positions do not necessarily recur after twenty-four hours, 

 and which are in no way affected by any rotation of the sidereal 

 heavens, and yet are wholly explicable on the hypothesis of the 

 eartVs rotation round its axis in twenty-four hours, and on no 

 other. To a person who views the pendulum experiment, the 

 rotation of the plane of its vibration is readily and speedily mani- 

 fest ; and because this may be shown to depend on the rotation 

 of the earth, it is not unnaturally designated a making the earth^s 

 rotation visible. We do not, however, apart from reasoning, 

 attribute the effect observed to the motion of the earth, any more 

 than we do the motion of the stars about us to that cause ; for 

 what we appear to see is strictly a motion of the plane of vibra- 

 tion round the zenith as a pole. It may suit the purpose of 

 popular explanation to say that the plane of tlie pendulum's 

 vibration remains unchanged while the earth rotates under it ; 

 but a little consideration shows that this is not strictly true, and 

 the conception of what does take place becomes more difficult 

 than in the case of the apparent motion of the heavens, since the 

 pendulum being carried at its point of suspension with the earth, 

 appears to be one with it. But though the earth's diurnal 

 rotation is less directly proveable in this way, it is far more con- " 

 clusively so than it is by the motion of the stars. In these last, 

 the motion having existed from the commencement of all things, 

 might have been originally impressed as well as that of the 

 earth ; but with the pendulum set in motion by human agency, 

 and continuing to vibrate without solicitation to the right hand 

 or left, on the supposition of the earth being at rest, no such 

 jipparent rotation could be brought about on any known physical 



