Isochronous Clocks. 465 



thought my time very ill applied in attempting to regulate those 

 astronomical clocks (with which I have been engaged) to that 

 degree of nicety to which of late years I have been accustomed, 

 had they been on such flimsy fixtures as those in question. The 

 two .'locks, the rate of whose going and keeping so closely to- 

 gether I gave you, were free of every floor, or of any elastic 

 board whatever, were s'trongly attached to a firm wall, and every 

 part connected with the pendulums uncommonly well bound, 

 particularly in that of their suspensions, so that any extraneous 

 weight, or any motion on the floor, could not possibly affect them, 

 nor was it possible that the motion of either pendulum could 

 have affected that of the other. It is nevertheless wonderfiil 

 how the motion of a jiendulum mav be affected, even where 

 every part of the fixture of it is such, that little or no doubt can 

 remain of its not being strongly fixed ; and yet 1 have made their 

 rate alter not a little by afterwards forcibly driving home for a 

 second time the screws of the fixtures, in order to be certain that 

 all was firm and secure, when I well knew that the first fixing 

 was much beyond that of any pendulum which had come under 

 my notice. The consequence which followed the second fixing 

 here was quite natural, the arc of vibration being a little in- 

 creased to what it was before. There is no man in the kingdom 

 who has paid that attention to the firm fixing of a clock pen- 

 dulum which I have done, and none know better the great ad- 

 vantages of it. The second turret clock which I made about 

 twenty-eight years ago, had the scapement part of it in aj'rame 

 separate from that of the clock, W'hich together with the pendu- 

 lum (whose ball a sphere about 70 lbs. weight) were firmly at- 

 tached to the wall of the church, and at a little distance from 

 the clock itself* : the advantage gained by this was not ob- 

 tained but at some expense. There is a mistake made in Mr. 

 De Luc's paper regarding Harris's pendulum clock being erected 



* Tliis clock, after having been brought to mean time, was carefully ob- 

 served from time to time by means of a sun-dial, which was correctly put 

 up close by the Observatory at Hawk-hill and by those concerned with the 

 Observatory, (I not having then the advantage or use of a transit instru- 

 ment,) and did not deviate thirty seconds from mean time during the course 

 of eight months. Not that I thiiik much of such trials, or the comparing the 

 going of a clock with a sun-dial, where nice observations are required ; yet 

 allowing the error to be even the double of ivhat the result gave, it cannot 

 be called great. Seeing the good going of tiie clock, the person who had 

 the charge of winding it up was requested to pay particular attention to it, 

 and by no means to neglect the winding of it. However, this request was 

 not strictly complied with, and the clock was one day unfortunately forgot, 

 and allowed to run down. This circumstance, and others which soon af- 

 terwards supervened, made me in future to bestow less attention to it than 

 It otherwise merited. The pendulum-rod of this clock was a wooden on^, 

 156'8 inches in length. 



Vol.45. No. 206. J««e 1815. Gg , in 



