Experimenis on the Vibrations of Pendulums. 279 



an important service. This, however, was but a secondary and 

 incidental effect of its application. 



The piece, which I have so named, is a brass tube about five 

 inches long, fitting the pendulum rod very nicely, and slit to form 

 a spring for about an inch at the bottom, so as to slide rather 

 stiffly on the rod. At the upper end of the tube is a clip, which 

 is made to embrace the suspending spring firmly by means of 

 two screws ; so that after the pendulum has been brought to the 

 proper length by the adjusting nut at the lower end of the rod, 

 the length of the acting part of the suspending spring may be va- 

 ried at pleasure, without in the least altering the length of the 

 pendulum, by merely sliding the isochronal piece up or down the 

 rod, and tightening the screws of the clip. 



I also provided five springs of different degrees of strength, and 

 a silken string, by which, in the first experiments, the pendulum 

 was suspended. 



The pendulum used was an uncompensated one, but in each 

 experiment it was adjusted to nearly the proper length for mean 

 time. 



Commencing with the silken thread, or rather two parallel 

 threads, one behind the other, I suspended the pendulum within 

 the case of a clock, perfectly detached from the works, no main- 

 taining power being applied. 



Each degree of the scale on which the arcs of vibration were 

 noted, was nearly -8 of an inch in length, and a degree was sub- 

 divided into twenty equal parts. 



I drew the bob aside 2°, and leaving it to vibrate by its own 

 gravity, I found the arc of vibration was reduced from 2° to 1°, 

 and from 1° to ^°, in the times noted as under : — 



Arc of vibration from 2° to 1° in 20m. 15s. 

 Do. do. 1 to^ 23 6 



On repeating the experiment, the results were : — 



Arc of vibration from 2° to 1° in 21m. Os. 

 Do. do. 1 to i 24m. Os. 



Drawing the pendulum aside 1°, I found from five successive 

 trials that the arc of vibration was reduced to half a degree in the 

 times following : — 



