of the Ear tie 8 Motion of Botation. 105 



lum has acquired a state of rest, the silk thread is burnt at 

 some point of its extent, the noose which enclosed the sphere 

 falls to the ground, and the pendulum, obeying the sole force 

 of gravity, is set in motion, and exhibits a long succession of 

 oscillation, the plane of which soon experiences an appreci- 

 able displacement. 



" At the end of half an hour this displacement is such as 

 to be obvious ; but it is more interesting to examine the 

 phenomenon more closely, so as to be satisfied of the con- 

 tinuity of the effect. For this purpose a vertical point is 

 made use of, a kind of style mounted on a support which is 

 placed upon the ground, so that during its to and fro move- 

 ment, the sharp appendage at the base of the pendulum, 

 when it reaches the extremity of its arc of oscillation, almost 

 grazes the fixed point. In less than a minute the exact coin- 

 cidence of the two points ceases to exist, the oscillating point 

 becoming constantly displaced towards the left hand of the 

 observer, indicating that the deviation of the plane of oscil- 

 lation takes place in the same direction as the horizontal 

 component of the apparent motion of the celestial sphere. 

 The mean magnitude of this motion, compared with the time 

 occupied in its production, shews, conformably to the indica- 

 tions of theory, that in our latitudes the horizontal track of 

 the plane of oscillation does not complete an entire revolu- 

 tion in twenty -four hours. 



"To the politeness of M. Arago, and to the intelligent 

 zeal of our able instrument maker, M. Froment, who has so 

 actively seconded me in the execution of this undertaking, 

 I am indebted for being able to repeat this experiment 

 upon a larger scale. Taking advantage of the lofty transit 

 room of the Observatory, I have been enabled to give a length 

 of eleven metres to the wire of the pendulum. The oscilla- 

 tions are thereby rendered longer and slower, so that between 

 two consecutive returns of the pendulum to the starting point, 

 a sensible deviation towards the left becomes clearly percepti- 

 ble." * — Bibliotheque Universelle de Geneve^ Mars 1851. PhiL 

 Magazine^ vol. i., 4th series. No. 7, p. 575. 



* This famous experiment has been repeated in various forms, and success-' 

 full)', by many competent authorities in this country. — Ed. Phil. Journ. 



