288 Mr Harvey on the effect of a magnet on a Pendulum. 



Art. XXV. — On a Remarkable Effect of a Magnet on the 

 Oscillations of the Pendulum of a Clock. By George 

 Harvev, Esq. F. R. S. Lond. and Edin. F. L. S. &c. 

 Communicated by the Author. 



In the latter end of the year 1822, my attention was drawn 

 to an experiment mentioned by Professor Cumming, in his 

 paper " on the connection of galvanism and magnetism," in- 

 serted in the second part of the first volume of the Transac- 

 tions of the Cambridge Philosophical Society ; viz. that the 

 application of a horse-shoe magnet, beneath the iron pendu- 

 lum of a small clock, occasioned an acceleration of the daily 

 rate. 



Desirous of repeating the experiment, I applied a power- 

 ful horse-shoe magnet as near as possible to the steel-spill or 

 index attached to the lower part of the weight of a compen- 

 sation pendulum composed of three bars of steel, and two of 

 a mixture of zinc and silver. The magnet was applied about 

 nine p. m., and, not anticipating any immediate effect, I left ft 

 to attend to some other pursuits. Having occasion, however, 

 to enter the room again about midnight, 1 found, to my great 

 astonishment, that the clock had stopped. The first impres- 

 sion on my mind was, that I had accidentally stopped it while 

 adjusting the position of the magnet ; but, on looking at the 

 minute hand, which indicated eighteen minutes after nine, and 

 recollecting that I had quitted the room about four or five 

 minutes after that hour, I began to suspect, that the action of 

 the magnet had suspended the oscillations of the pendulum. 



To determine this interesting point, I communicated mo- 

 tion to the pendulum, and, after the lapse of a few minutes, 

 observed a sensible diminution in the amplitude of its vibra- 

 tion ; and, at the end of twelve minutes after the oscillations 

 commenced, the arc of vibration was so much reduced, as to 

 suspend the beats of the clock ; and, in a short time after, the 

 continually diminishing arcs of vibration vanished altogether, 

 the pendulum being reduced by the action of the magnet to a 

 perfect state of rest. 



Feeling now perfectly satisfied, that the stopping of the 

 clock was due entirely to the action of the magnet, I proceed- 



