[ 521 . ] 
likewife applied this combination of wires of brafs 
and fteel, to prevent any alterations by heat and cold. 
In the year 1726, he went on board one of His 
Majefty’s fhips of war with this machine to Lisbon, 
and returned, where this machine was feen by every 
curious and ingenious perfon, who were pleafed to 
go to his houfe. Since that time, he has made two 
more of thefe machines or clocks for keeping time at 
lea, in both which he has likewife this provifion, to 
prevent the effedts of heat and cold. 
An account of thefe curious machines, and of the 
many ingenious contrivances which Mr. Harrifon has 
made ufe of in them, for anfwering their intended 
purpofe, and alfo an account of the fuccefs of his 
voyage to Lisbon, and back again, is contained in an 
excellent fpeech of our worthy Prefident Martin 
Folkes, Efq; upon his delivering to Mr. Harrifon the 
gold medal of Sir Godfrey Copley ; which fpeech is 
inferted in the minutes of the Society in the year 
* 749 - 
Mr. John Shelton, who was the principal perfon 
employed by Mr. Graham in the making of agrono- 
mical clocks, informs me, that Mr. Graham, in the 
year 1737, made a pendulum confiding of three bars, 
viz.. one of fteel, between two of brafs, and that the 
fteel bar adted upon a lever, fo as to raife the pendu- 
lum, when lengthened by heat, and to let fit down, 
when fhortened by cold. This lever, which is very 
ftrong, refts upon a roller ; which roller is made 
moveable, fo as to adjuft the arms of the lever to 
their true proportion. The whole was made to be 
as free from fridtion, as poftible, in fuch a conftruc- 
tion. Mr. Graham made obfervations, by tranfits of 
U u u the 
