184 Messrs. Galbraith and Haughton on the Apsidal Motion 



of greatest tension at Guildford. Then in the Greenhurst line, 

 we see that where it is exhibited in greatest force, and its fea- 

 tures are best displayed almost in the axis of the Weald, it brings 

 up a long line of Weald-clay exposure from Greenhurst to Poyn- 

 ings. And at this part of its course two notable lines of trans- 

 verse fissure show themselves*. It heaves the gait in a saddle 

 at Waltham Park and the New Woods, and throws it back into 

 a synclinal at Hardham and Wiggonholt. At Bramdean it is a 

 chalk saddle, and at Winchester an open anticlinal valley of the 

 lower chalk. All this necessarily implies change of strike, and 

 of angle of inclination, which cannot take place beyond a certain 

 point without transverse fracture at the surface. 



Having now cleared the way for a recognition of the strict 

 relations of the chalk dome of Hampshire and Wiltshire with 

 the Weald denudation, I hope to be able in my next communi- 

 cation to proceed to the subject of transverse fissure and the 

 phsenomena of drainage; recapitulating and carrying forward 

 my former disquisitions on the simultaneous and tumultuous 

 operations of upheaval and aqueous abrasion. 

 [To be continued.] 



XXII. On the Apsidal Motion of a freely suspended Pendulum. By 

 Mei^ev. Joseph A. Galbraith and the Rev. Samuel Haughton. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



THE following investigation of the apsidal motion of a freely 

 suspended pendulum may be interesting to those of your 

 readers who have been engaged in verifying M. Foucault's ex- 

 perimental demonstration of the earth^s rotation. Some time 

 ago we undertook a course of experiments with that view ; and 

 although we arrived as a general result at a complete verification 

 of this remarkable experiment, we found considerable deviations 

 from the law of uniform angular motion. This led us to con- 

 sider the different disturbing forces, and if possible calculate 

 their effects, and thus eliminate them from our observations. 



The motion of a pendulum may be compared with that of a 

 point moving in a plane round a centre of force, whose intensity 

 is directly as the distance, if the amplitude of vibration be inde- 

 finitely small; but if this be not the case, we must consider the 

 motion as taking place in a spherical ellipse and disturbed by a 

 small force directed from the centre, and varying as the third 

 power of the distance. As the influence of this disturbing force 



* Viz. the river course of the Adur, and the Vale of Findon, the line of 

 the Worthing road. 



