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LXV. Intelligence and Miscellaneous Articles. 



foucault's pendulum experiment. 

 To the Editors of the Philosophical Magazine and Journal. 



Gordon's Hospital, Aberdeen^ 

 Gentlemen, July 1851. 



AS M. Foucault's experiment is now an engrossing topic in scien- 

 tific circles, I beg leave to forward a verification of it for this 

 place, lat. 57° 9' N., and to offer a few remarks tending to explain 

 some of the pha^nomena connected with it in a manner somewhat dif- 

 ferent from that usually adopted. 



Every experimenter is struck by a tendency of the pendulum to 

 get into an elliptical orbit, and is disposed to ascribe the ellipticity 

 to the imj)erfection of the apparatus, the resistance of the air, or some 

 Cause accidental and not essential to the exjieriment. But as a 

 greater or less amount of ellipticity sooner or later makes its appear- 

 ance in every instance, it would appear reasonable to infer that it 

 must proceed from some cause inseparable from the conditions of 

 the motion ; and on consideration, it is obvious that the path of the 

 pendulum from the very first will not be in a straight line across the 

 table, but in a curve approaching to an ellipse ; for the body, when 

 steadied at the circumference of the table and let go, is acted upon 

 by t\vo forces. Viz. gravity, which would carry it in a straight line 

 over the centre, and a lateral impulse derived from the rotatory mo- 

 tion of the circutnference of the table with respect to its own centre. 

 T^e Joint effect of these two forces will be to produce a motion in 

 ati elliptical or ellipsoidal orbit passing a little to the right of the 

 centre, and returning a little to the left of it. The point of the cir- 

 cumference, to which the body will return, will depend upon \yhether 

 the major axis of the ellipse is fixed or moveable. 



1. If the axis of the ellipse be fixed, the pendulum will return 

 to a point a little to the left of that from which it set out, and will 

 have ari apparent motion contrary and equal to the real motion of 

 thfe table. This is M. Foucault's experiment when successfully 

 performed. 



2. If the axis of the oi-bit move directly, i. e. from west to east at 

 the same rate as the circumference of the table, the body will return 

 to the point from which it was let go, and no deviation will be ob- 

 served. If the motion of the axis is direct and quicker than that of 

 the table, the body \Vill deviate from west to east with respect to 

 the cifcutoference. Both these effects are observed in conducting 

 the experiment, if the pendulum either by accident or design receive 

 a slight impulse to the right. 



3. If the axis or line of apsides of the orbit have a retrograde mo- 

 tion, the pendulum will deviate from east to west, and at a higher 

 rate than that of the real motion of the table. This result is ob- 

 served in most of tlie eiperimcnts, even those conducted with the 

 greatest care. From the paper contributed by Mr. Bunt of Bristol 

 to a recent Number of your Magazine, it appears that the observed 



