JE^'FECT OF ATTRACTION ON THE GOING OF CLOCKS. QJ 



l^eepingtbis arc perfectly for above two weeks, it surprised me, 

 and even mortified me not a little, to find no constancy in the Ee^an to diml- 

 , ^ • I . J- • t I J u "''^''' '*^s arc of 



arc even here, notwithstanding very sangume hopes had been vibration in 



entertained of it. One morning it was observed to have come three weeks, 



in a little, which afterward it did gradually more and more for 



8ome time, from a maximum to a minimum, and vice versa, and after a 



until it had regained its original extent of arc, which it kept on, ■J^^^^^^'^^*®** 



till the same circumstances came again in the way to disturb it. 



Although I saw tliis, and was in some degree convinced, that 



this must be owing to the attraction of the v»'eight for the pen- This presumed 



dulum ; yet I would not rest altogether satisfied without again ^° ^^'^'^ ^f°"^ 



..,,,,, ,. . , . , f- , the weight at- 



exammiug the clock, lest sometnmg might be there, which tracting the 



tended to give rise to this inequality of the arc of the pendu- pendulum. 



lum's vibration. But on examination, there was evidently no 



cause, that could in the smallest degree be suspected, for this. 



In constructing the clock, attraction was suggested by a very 

 ingenious friend, on an idea taken from the experiments that foreseen an" 

 had been made by Mr. Cavendish : and accordingly the barrel guarded 

 was so contrived, as to throw the weight, when it came as low ^"'^Tl-e-t aHv 

 down as the pendulum ball, the farthest then possible from it. 

 The weight is about 27lb. j and the pendulum, which is a mer- 

 curial one, has about lOlb. of mercury in a glass jar or hollow 

 cylinder. In order to be more convinced in this matter, tha 

 clock was again wound up, and during the time of the first ten 

 days or a fortnight it kept the arc of vibration constantly the 

 lame, and its rate of time was somewhat less than +0'l" 

 per diem j when the weight had got down, and partly opposite 

 to the cylinder of mercury, the arc of vibration began to come 

 in, and the clock gained in the mean time from less to more, 

 ©ven to five seconds in one of those days ; when the v?eight had 

 got below the pendulum or cylinder of mercury, the former 

 arc of vibration was regained, and its rate of time also. The 

 full extent of the arc of vibration is about one degree eleven 

 minutes on each side the point of rest, of this it lost about six 

 -minutes when at its least extent. 



There was another clock observed, which goes a month, has Another dock 

 •somewhat of the common scapement to it, and a compensation gij^ij^r man-* 

 pendulum of Ward's form, which I think Is a vevy excellent ner. 

 one. The arc of vibration is about three degrees six minutes 

 on each side the point of rest, the weight of the pendulum ball 



about 



