278 Experiments on the Vibrations of Pendulums. 



inertia and friction, as, in this case, the influence of any other 

 force is more obvious. Any two different planes or even the 

 same might be employed by a little modification of the process, 

 but those specified are most eligible, as in them the forces aff'ect- 

 ing the position of the needle present the greatest disparity. 



U. S. Ship Independence, Jan. 28, 1839. 



Art. XIY. — Results of Experiments on the Vibrations of Pendu- 

 lums^ loith different suspending springs ; being the substance 

 of a paper by W. J. Frodsham, F. R, S., 7^ead before the Royal 

 Society, June 21, 1838. Forwarded for insertion in this Journal. 



The experiments of which I am about to give an account, and 

 from which I propose to draw some practical conclusions, were 

 undertaken with a view to determine whether some particular 

 condition of the suspending spring of the pendulum, with respect 

 either to its length, its strength, or both, might not cause it, with 

 a lighter maintaining power, to produce a given arc of vibration, 

 or, with a given maintaining power, to produce a greater arc of 

 vibration than any other ; and at the same time to ascertain 

 whether some practical means might not be devised for making 

 unequal arcs of vibration in the ordinary pendulum, correspond to 

 equal intervals of time. 



My attention was drawn to the subject many years ago, when, 

 having replaced the spring of a turret-clock by a stronger one, I 

 found the arc of vibration materially altered. 



Having often reflected upon the subject, I at length resolved to 

 make some experiments to satisfy my mind respecting it ; and I 

 accordingly had made for the purpose a lenticular pendulum bob 

 of about fourteen pounds weight, a cylindrical rod passing through 

 it, with a nut working on a screw at the lower end, and support- 

 ing the bob. 



The upper end of the rod was slit to receive the spring ; and 

 the spring and the rod were attached to each other by a pin pass- 

 ing through a hole in both. 



But before fixing the pin, what I call an isochronal piece was slid 

 over the top of the rod, and if this part of the apparatus had served 

 only to attach the rod and spring more firmly together, and prevent 

 any wavering motion of the pendulum, it would have rendered 



