\\\\\\{y< \\\' \rui:>iV V 



[ 37 ] 



)t 



VI . Pendulum Eooperiments. By Thomas G. Bunt. '^^ 

 To the Editors of the Philosophical Magazine and Journal. ^ 



Gentlemen, Bristol, June 11, 185T. 



THE series of pendulum experiments detailed in my last letter 

 I have now somewhat extended, and arranged more system- 

 atically than before. The result of the whole is shown in the 

 following summary : — 





I 



fffVl^g 



The arc of vibration usually given to the pendulum on starting 

 it_, was about nine feet^ which in half an hour decreased nearly 

 one-third. The mean rate of apsidal motion of these arcs, on 

 their becoming elliptical (as they generally did in the course of 

 a few minutes), 1 had found to be about y^ths of a degree per 

 hour to Y^o^h of an inch of ellipticity, or length of half minor 

 axis. I had assumed that this rate would hold good as the arcs 

 become shorter, provided both axes diminished in the same ratio^ 

 and consequently that it would increase when the arc shortened 

 and the ellipticity continued the same. A few experiments on 

 short arcs (which I had begun to prefer to long ones) soon con- 

 vinced me that this assumption was directly contrary to the fact ; 

 and that with a given length of minor axis, the progression of 

 the apsides was slower as the arc of vibration decreased. This 

 discovery, together with other manifest advantages attending 

 short arcs, determined me on confining myself entirely to them 

 in future ; and I accordingly substituted instead of my old circle, 

 a new one of only half the diameter. My next improvement 

 was in the mode of suspension ; a suggestion for which I am 

 indebted to a scientific friend, who made the apparatus for me. 



A brass screw, about li inch long and | inch in diameter, 

 was sawn through the greater part of its length into four sec- 

 tions or quadrants, meeting in the axis. The screw was firmly 

 centred into a brass disc, and before having the thread cut upon 



