Intelligence and Miscellaneous Articles. 577 



sists of steel strongly hardened by the action of the draw-plate ; 

 its diameter varies from ^^ths to y^ths of a millimetre ; it extends to 

 the length of two metres, and to its lower end is attached a sphere 

 of brass turned and polished, and which moreover was hammered so 

 that its centre of gravity should coincide with its centre of form. 

 This sphere weighed five kilogiammes, and a sharp prolongation 

 was fixed to it, apparently forming a continuation of the suspending 

 wire. 



" When it is wished to make the experiment, the first thing to be 

 done is to put an end to the torsion of the wire and the rotatory os- 

 cillations of the sphere. Then, for the purpose of displacing it from 

 its position of equilibrium, it is inclosed in a noose of silk thread, the 

 free extremity of which is attached to some fixed point in the wall, 

 at a small height above the ground. According to the length given 

 to this thread, the displacement of the pendulum and the magnitude 

 of the oscillations which it may be wished to communicate to it, are 

 an"anged arbitrarily. In general, in my experiments, these oscilla- 

 tions, at the beginning, comprised an arc of from 15 to 20 degrees. 

 Before proceeding further, it is requisite to deaden by some obstacle, 

 gradually withdrawn, the oscillatory motion still exercised by the 

 pendulum while restrained by the thread and suspending wire. As 

 soon as the pendulum has acquired a state of rest, the silk thread 

 is burnt at some point of its extent, the noose which inclosed 

 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 oscillations, the plane of which soon experiences an appreciable 

 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 continuity 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 movement the sharp appendage at the base of the pen- 

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

 grazes the fixed point. In less than a minute the exact coincidence 

 of the two points ceases to exist, the oscillating point becoming con- 

 stantly displaced towards the left-hand of the observer, indicating 

 that the deviation of the plane of oscillation 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, shows, conformably to the 

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

 the plane of oscillation does not complete an entire revolution 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 



