M 



Eofjal Socie({/. 



Second Set. Time observed when deination amounted to given 

 angles. Boll an oblate splieroidy weighing ^0 pounds. Suspen- 

 sion catgut. 



Direction at orisin. 



3. E.andW.| 



4. N. and S. | 



Minute* of 



a. 15-38 



b. 23-40 



a. 150 

 *. 24-44 



Demtion. 



Left. Right. 



Chord at 

 origin. 



ft. 

 14 



14 



EUipticity. 



Direction. Minor 



None ob served. 

 None ob served. 



t 



Very mjinute. 

 Left. \ inch. 



Neglecting the ellipticity in these experiments, the results are — 

 Deviation in one hour fiom 



^•"""^^■•""^ "•J^-|}mea„12-2+. 



^•'""'S-line «;}|0j„eanl2-0+. 



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- 

 ing the deviation when the motion in the ellipse was to the right, 

 and diminishing it when it was to the left. In most azimuths the 

 elliptical motion was to the left. In the following example its effect 

 was followed for an hour to the right. 



* Doubtful. 



