2 On the Theory of 



I am aware of, and the chief mention I have found of the principle 

 of his escapement is in the works of the French authors *. 



Thiout l'a'me, in his Traite de VHorlogerie, 4to, Paris, 1741, on 

 the subject of Escapements, Vol. 1st, page 103, thus expresses 

 himself: — " Fig. 19, (Plate 43, Vol. 1st,) is a dead escapement for 

 clocks, as made by Mr. Graham, clock-maker, of London. The 

 rule I have discovered for making it, and which I apprehend to 

 be a good one, is to place the center of the anchor at the distance 

 of one diameter of the wheel from the wheel," (that is a diameter 

 and a half of the wheel from its center,) " as shewn in the figure. 

 The center of the anchor must be placed upon the perpendicular 

 line, passing through the center of the wheel, and the wheel cut 

 into thirty teeth, beginning from the above-mentioned perpendi- 

 cular line ; and the teeth which suit the best must be chosen to 

 determine the place of an arc drawn from the center of the anchor 

 upon which to form the pallets, which must be so made that the 

 seconds hand does not recoil." Here follows a description of the 

 action of the escapement. 



From the above it is evident, that M. Thiout's knowledge of 

 this escapement was very limited. 



The subject of the dead escapement is entered into at some 

 length by F. Berthoud, F.R.S., of Paris, the author of several 

 horological works. In his Essai sur VHorlogerie, 4to, Paris, 1763, 

 Tom. 1, Premiere Partie, Chap. xxi. No. 397, page 129, he thus 



* I fully expected some account of this escapement in the Transactions of 

 the Royal Society, of which Mr. Graham was a member : but by reference to 

 the Index of the transactions, there is no mention of Clock Escapements ; at 

 which 1 am the more surprised, as there is a communication from Mr. Graham 

 on the subject of his invention of the Mercurial Pendulum, and the mea- 

 suring the lengths of pendulums at different places. Mr. Graham was the 

 immediate successor to Tompion, and the art of Clock and Watch-making is 

 so much indebted to him for its advancement, that I consider it due to his 

 memory to insert the following memorandum. 



He was born in 16*5, was elected an Assistant of the Court of the Company 

 of Clock-make«s of the city of London the 18tli April, 1716, and served the 

 office of Master of the Company 1721 and 22 ; was elected a Fellow of the 

 Royal Society the 9th March, 1728, and died the 16th November, 1751. His 

 remaius were interred in the aisle of Wesminster Abbey. 



