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In June, 1752, Mr. John Ellicott gave in to the 
Royal Society a paper, containing the defcription of 
a pendulum, confiding of two bars, one of brafs, and 
the other of iron, fattened together by fcrews, with 
two levers in the bob of the pendulum, fo contrived, 
as to raife and let down the bob, by the expanfion 
and contraction of the brafs bar ; and alfo to adjutt 
the arms of the levers to their true proportion *. He 
lays, that he ttrtt thought of thefe methods of apply- 
ing bars of brafs and iron to prevent the irregularities of 
a clock, arittng from the different lengths of the pen- 
dulum, by the effects of heat and cold, in the year 
1732 j and that he put this his thought in execution 
in the year 1738. 
In the year 1 743, I bought a clock of Mr. Graham, 
which he had kept going for two years before. This 
clock has a pendulum, compounded of wires of brafs 
and tteel, in the manner of Mr. Harrifons combina- 
tion. It has alfo a provifion in the bob, to adjutt the 
wires, in cafe they happen to be too long. When I 
firft took notice of this contrivance or provitton in the 
bob, I afked Mr. Graham the reafon of it $ who told 
me, that, having obferved fome inequalities in the 
motion of the clock, he imagined, that they arofe 
from the wires being fomewhat too long j and there- 
U u u 2 fore 
* He has alfo given us in the fame paper another conftrudlion 
of a pendulum to prevent the effects of heat and cold, confifting of 
two bars, one of brafs, and the other of iron ; the brafs bar acting 
upon a lever, at the end of which is fattened the pendulum, the 
whole fo conftru&ed and contrived, as to raife the pendulum, when 
it is lengthened by heat, and to let it down* when fhortened by 
cold. 
