79 



First Set. Deviation observed after given intervals of Time. Ball 

 a prolate spheroid, weighing eight pounds. Suspension softened 

 catgut. 



Direction at origin. 



Minutes 



Deviation. 



Chord at 



Ellipticity. 



of time. 



Left. 



Right. 



origin. 



Direction. 



Minor axis. 



1. E. andW.... 



60 









13 



ft. 

 14 



None ob 



served. 



2. N. and S. ... 



45 







14 



None ob 



served. 



Supposing no ellipticity to have existed in these experiments, the 

 results are — 



Deviation in one hour from E. and W. line to right 13°'0 



N. and S. „ 15°'3 



Second Set. Time observed when deviation amounted to given 

 angles. Ball an oblate sjiheroid, weighing ^0 pounds. Suspen- 

 sion catgut. 



Direction at origin. 



Minutes of 



De\dation. 



Chord at 



Ellipticity. 



time. 



Left. 



Right. 



origin. 



Direction. 



Minor axis. 



3. E. and W.j 



a. 15-38 



b. 23-40 





o 



3 

 5 



ft. 

 14 



None ob 

 None ob 



served, 

 served. 



4. N. and S. | 



a. 15-0 



b. 24-44 





3 

 5 



14 



Very m 

 Left. 



inute. 

 ^ inch. 



}|*^jmeanl2°-0 + . 



Neglecting the ellipticity in these experiments, the results are — 

 Deviation in one hour from 



E. and W. line a. 



b. 



N. and S. line a. 



b. 



For obvious reasons — the force maintaining the pendulum plane 

 being greatest in the beginning of the sweep (when the versed sine 

 of the arc is greatest), and the action of the elliptical swing then 

 least — the deviations in the first portions of the hour appear likely 

 to be more correct than the average of the whole hour. 



The suspension was now changed from softened catgut to un- 

 twisted silk. From some disarrangement connected with this change 

 it happened that ellipticities were generated in every experiment, 

 and nearly all were abandoned as useless on account of the great 

 dimensions of the ellipse, which, growing as the arc of vibration 

 lessened, sometimes acquired a minor axis of above three inches. 

 Whatever the direction of the movement in the ellipse, its effect was 

 to rotate the pendulum plane in the same direction ; thus augment- 



