VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 301 



such an experiment, and was satisfied with their result. But, not seeing clearly 

 how such a pendulum could be connected to a piece of mechanism, to number the 

 vibrations without affecting them, I dropped the idea for that time. I learnt how- 

 ever, some time afterwards, that Mr. John Whitehurst, a very ingenious person, 

 had been in pursuit of the same object with better success, and had contrived a 

 machine fully corresponding to his expectations and my wishes. This he afterwards 

 explained to the world, in a pamphlet, entitled, " An Attempt to obtain Measures 

 of Length, &c. from the Mensuration of Time, or the true Length of Pendulums;'* 

 published in 1787- Mr. Whitehurst having there done all that related to the 

 standard measure of length, and suggested that of weight, it appeared to me that 

 it remained only to verify and complete his experiments. 



For this purpose, by the assistance of Dr. G. Fordyce, who, at Mr. Whitehurst's 

 death, had purchased his apparatus, I was furnished with the very machine with 

 which Mr. Whitehurst had made his observations. I also procured to be made, 

 by Mr. Troughton, an excellent beam-compass or divided scale, furnished with 

 microscopes and micrometer, for the most exact observations of longitudinal mea- 

 sure: as also a very nice beam or hydrostatic balance, sensible with the - T l 0(i of a 

 grain, when loaded with 61b. Troy at each end. Mr. Arnold made me one of his 

 admirable time-keepers, in order to carry time from my sidereal regulator in my 

 observatory, with which it was adjusted, to the room where I had fixed Mr. White- 

 hurst's pendulum; and who, having taken a journey from London into Warwick- 

 shire, was so good as to assist in the beginning of these experiments. Thus 

 equipped, I went to work in the latter end of Aug. 17 96, when the temperature 

 was about 60°, first to examine the length of the pendulum; when, to my great 

 mortification, I found that the thin wire, of which the rod consisted, was too weak 

 to support the ball in a state of vibration; and that, after 15 or 20 hours action, 

 it repeatedly broke. The same misfortune attended my trials with 3 other different 

 sorts of wires that I had obtained from London. Whether this accident happened 

 from any rust in the old wire, or from want of due temper in the new, or from its 

 being too much pinched between the cheeks, I cannot tell: I can only observe, 

 that all the wires that I used were considerably heavier, and therefore probably 

 stronger, than what Mr. Whitehurst mentions, viz. 3 grains in weight for 80 

 inches in length; nay, mine proceeded as far as from 5 to 6 grains for that length, 

 and yet I could never get it to support the ball during the whole period of my 

 experiment. This being the case, and being in the country, far removed from the 

 manufactory of this fine wire, I was reluctantly compelled to relinquish this part of 

 the operation to some more favourable opportunity. In the mean while however, I 

 thought it desirable to measure the difference of the lengths of Mr. Whitehurst's 

 pendulum from his own observations; for, very fortunately, the marks that he had 

 made on the brass vertical ruler of his machine were still visible; and this interval, 

 which he calls " 59.892 inches," I determined, on my divided scale made by 

 Troughton, from Mr. Bird's standard, to be = 59.89358 inches, from a mean of 



