286 PHILOSOPHICAL TRANSACTIONS. [annO 175 J. 



perience of several years, during which the clock was kept constantly going, he 

 found that the clock was liable to sudden starts and jerks in its motion. Of this 

 he informed Dr. Bradley, Mr. Bliss, Mr. S. and several other gentlemen. This 

 clock still remains in Mr. Graham's house, in the possession of his executors. 



Mr. S. had been informed, that one Mr. Frotheringham, a quaker, of Lin- 

 colnshire, caused a pendulum to be made, consisting of 2 bars, one of brass, and 

 the other of steel, fastened together by screws, with levers to raise or let down 

 the ball ; and that these levers were placed above the ball. This clock Mr. S. 

 had seen, and was told by the maker, Mr. John Berridge, that the pendulum of 

 it was made in 1738 or 1730, and that the dial-plate of it was engraved at Mr. 

 Sisson's house in 1738 : and this clock is in the possession of Mrs. Gibson, in 

 Newgate-street, who has had it ever since the year 1739- 



In the Hist, of the Royal Acad, of Sciences at Paris, for 1741, there is a me- 

 moir of M. Cassini, in which he describes several sorts of pendulums for clocks, 

 compounded of bars of brass and steel, and applies a lever to raise or let down the 

 ball of the pendulum, by the expansion or contraction of the bar of brass. He 

 has also given in the same memoir, a problem for finding the proportion which 

 the two arms of the lever should have, to answer the intended purpose ; and 

 also a demonstration of it. 



In June, 1752, Mr. John Ellicot gave in to the Royal Society a paper, con- 

 taining the description of a pendulum, consisting of 2 bars, one of brass, and 

 the other of iron, fastened together by screws, with 2 levers in the pendulum 

 ball, so contrived as to raise and let down the ball, by the expansion and con- 

 traction of the brass bar ; and also to adjust the arms of the levers to their true 

 proportion.* He says, that he first thought of these methods of applying bars 

 of brass and iron to prevent the irregularities of a clock, arising from the dif- 

 ferent lengths of the pendulum, by the effects of heat and cold, in 1732; and 

 that he put his thought in execution in 1738. 



In 1743, Mr. S. bought a clock of Mr. Graham, which he had kept going 

 for 2 years before. This clock has a pendulum, compounded of wires of brass 

 and steel, in the manner of Mr. Harrison's combination. It has also a provision 

 in the ball, to adjust the wires, in case they happen to be too long. When 

 Mr. S. first took notice of this contrivance or provision in the ball, he asked Mr. 

 Graham the reason of it ; who told him, that having observed some inequalities 

 in the motion of the clock, he imagined that they arose from the wires being 

 somewhat too long ; and therefore added this contrivance, to adjust the length 



• He has also given, in the same paper, another constmction of a pendulum to prevent the effects 

 of heat and cold, consisting of 2 bars, one of brass, and the other of iron ; the brass bar acting on a 

 lever, at the end of which is fastened the pendulum, the whole so constructed and contrived, as to 

 raise the pendulum, when it is lengthened by heat, and to let it down, when shortened by cold. — Orig. 



