[5 H] 
fore added this contrivance, to adjuft the length of 
the wires ; but that, when he had done this, he 
found inequalities hill remaining $ and therefore juftly 
concluded, that they arofe from the difference in the 
fridtion of the different parts of the clockwork, oc- 
cafioned by the differences in the fluidity of the 
oil, &c. 
From what has been faid above, it appears, that 
the improvement of clocks, by a contrivance to pre- 
vent their inequalities ariflng from the different 
lengths of the pendulum, in different feafons of the 
year, by the effedts of heat and cold, was firff thought 
of, and executed, by Mr. George Graham ; and that 
the application of wires or bars of two metals, which 
have different degrees of expansion or contradtion, to 
prevent the fame inequalities, was alfo firffc thought 
of by Mr. Graham, and flrft executed by Mr. John 
Harrifon, without the leaft knowlege of what Mr. 
Graham had done before him. 
LXXXIX. A Letter from Mr . Henry Eeles, 
to the Royal Sdciety, concerning the Caufe 
of Thunder. 
Gentlemen, Lifmo:e > IreIa nd, June 18, 
1752. 
Read Nov. 7, / | ^HE greateff men of mod ages hav- 
jf ing thought it worth the while to 
inquire, what was the caufe of thunder ; and the 
world feeming to acquiefce in an hypothefis fub- 
ferib’d by fome great modern names, it muff appear 
prefumptuous in me, to offer you fome thoughts for 
a theory intirely new (at leaft it is fo to me) unlefs 
I can fhew, that the former hypothefes are ill- 
grounded, 
