V.~\?i'-* r • - Royal Institution. 561 



Philosophical Magazine, coincides with the opinion originally 

 entertained by Prof. Potter himself; but as he now disclaims 

 that opinion, and attaches some mysterious meaning to the 

 terms " attributed cube," " area for pressure," &c., it rests with 

 him to explain by some argument better than the repetition of 

 a mere assertion, why he has changed his mind ; and to give a 

 clearer definition than he has yet done, of the precise meaning 

 of his tenns. 



I am. Gentlemen, 



Yours, &c.. 

 Trinity College, Dublin, Samuel Haughton. 



May 26, 1851. . 



LXXXIII. Proceedings of Learned Societies. 



ROYAL INSTITUTION. 



May 9, /~\N the recent experiment showing the Rotation of the 

 1851. \J Earth by means of the Pendulum. By the Rev. Baden 

 Powell, M.A., F.R.S., F.R.A.S., F.G.S. 



The experiment alluded to has been the subject of so much popu- 

 lar notice at the present time, that it would be needless to go into a 

 particular description of its nature or object. If fully verified, the 

 result would however hardly amount to any mor^ palpable proof to 

 the senses than other astronomical phgenomena afford ; in this case, 

 as well as in those, the conclusion is equally derived from reasoning 

 on the actual appearances. 



An idea of such an effect seems to have occurred long ago, and 

 is mentioned in a paper in the Phil. Trans., 1742, No. 468, by the 

 Marquis de Poli, in the course of some observations on the pendulum 

 of a different kind. He remarks, " I then considered (adopting the 

 hypothesis of the earth's motion) that in one oscillation of the pen- 

 dulum, there would not be described from its centre perfectly one 

 and the same arc in the same plane ;" but he does not pursue the 

 subject, as being foreign to his immediate object. 



It appears also (see Comptes Rendus, 1851, No. 6) that in 1837 

 Poisson had hinted at such an effect, but supposed it of insensible 

 amount. 



To some minds difficulties present themselves in the first instance, 

 which are easily removed by a few simple illustrations. In the first 

 place, the deviation from parallelism to itself, of tlie meridian of any 

 place, during the rotation of the earth, is a simple geometrical question 

 easily determined, and the inclination expressed by a trigonometrical 

 formula. In the next place, the independence of the motion of the 

 pendulum, notwithstanding that the point of support is carried along 

 with the earth in its rotation, and that the whole seems to form a 

 part of the earth, is a point easily elucidated by very simple experi- 

 ments, in which the vibration of a small pendulum is seen to continue 

 parallel to itself notwithstanding a motion given to the point of 

 support; the effect being in fact only a simple consequence of the 



