AT THE MADRAS OB&ERVATORY. '^m 



weight.^ I suspended, for some time, a four pound weight, to about six 

 feet length of this string; and on removing it, I fastened, in its stead, a 

 ball of cast lead, of i, 34« inch diameter, weighing 7. 384 oz. troy 

 weight, with which the experiments were made. The insertion was con- 

 trived, by boring a very small hole, of a sufficient depth, towards the cen- 

 tre of the ball, into which it was introduced, and secured by a small pin, 

 strongly driven, and then filed even with the surface of the sphere, so 

 that there was no loop, and the whole length was uniform.^') 



6. The pendulum of experiment being thus prepared, I fastened it 

 to an iron head, made at one end in the shape of a common nail, and at 

 the other in that of an oblong square; so that, when fixed, it proje6led 

 about two inches from the wall, and was perfe6lly immovable, 



7. Near the extremity of this square, I caused a very small hole to 

 he perforated, just large enough to admit the thread, so that the axis of 

 motion of the pendulum should be exactly at the lower surface of the 

 iron head, 



8. This apparatus was fixed against the northern wall of the Observa* 

 tory, and close by the clock, which keeps mean time; an excellent piece, 

 made by Haswall, who brought it out to Lidia, and placed it himself 

 where It now stands. 



9. Several concentric circles, of a radius nearly equal to the pendulum 

 of experiments, were drawn against the wall, from the iron head as a 

 rcentre. These were divided into quarter inches, in order to determine the 

 arcs of vibration. ■ 



(4) Weiijhctl by Mr. Rokbuck, in the assay scales at the Madras mint. 



(5) It was first weighed with the string in bulii ; then the string \vas weighed separately. 



