650 I'HILOSOPHICAL TRANSACTIONS. [aNN0 1734. 



sure be reduced to the same length, whenever there should be occasion to 

 remove the clock from one place and set it up in another. 



This clock, being chiefly designed for astronomical observations, had no 

 striking part, and its pendulum was adjusted to such a length, that in London 

 it vibrated seconds of sidereal, and not solar, time. When it was finished, 

 Mr. Graham fixed it up in a room, situated backward from the street, and on 

 the northside of his house, to prevent its being disturbed by coaches, or other 

 carriages that passed through the streets, and that it might be as little affected 

 by the sun as possible. Having set it a-going, he compared it with the transits 

 of the star Lucida Aquilae over the meridian, which passed, by the clock, 

 1731, August 20. . at. . S'' 59*" 15' 



11. . at. . 8 59 18 



23. . at. . 8 59 204^ Hence it appears that the clock gained 

 12 seconds in 10 apparent revolu- 

 tions of the star. 



In order to estimate how much the pendulum may be lengthened by greater 

 degrees of heat, or how much slower the clock would go on that account, 

 when removed into a warmer climate, a thermometer was fixed by the side of 

 it; and between the hours of 10 and 1 1 o'clock in the morning, and at night, 

 notice was taken at what height the spirits stood, and the mean height for each 

 day was as follows: 



days therm. 

 1731, Aug. 20. . 274- div. 



27. . 27^ Hence the mean height 



28. . 27-i- for all these days was 

 29. . n\ about 28i divisions. 

 30. . 27A 



The clock-weight, that keeps the pendulum in motion, is 12 lb. lO^oz. and 

 is to be wound up once a month. The weight of the pendulum itself is 17 lb.; 

 and, during the time that the clock was compared with the transits of the star, 

 it vibrated each way from the perpendicular 1° 45'. The magnitude of the 

 vibrations was estimated by means of a brass arch, which was fixed just under 

 the lower end of the rod of the pendulum, and divided into degrees, &c. 



August 31, Mr. Graham took off the weight belonging to the clock, and 

 hung on another of 61b. 3 oz. and with this weight the pendulum vibrated only 

 1° 15' on each side; and the clock went 1^ second slower in 24 hours, than 

 when its own weight of 12 lb. 10-i-oz. was hung on. 



