382 INVENTION OF THE BALANCE SPRING. 



Farther parti- " It is very true, that in IZ^S, M.L.R. presented a 'scapemetit 

 marks ^""^ ^^' '' *^**^^ Academy ; it is very true, that the Academy said then, 

 " that the idea of it seemed nevs'. What was this 'scapement ? 

 " The Academy does not tell. But can M. L. R. assure us 

 " now, supposing that this was a 'scapement with free vibra- 

 " tiolis, that the idea of it was new? Can he require that we 

 ** should believe that his'scapement of 1748 was t/iejirst of this 

 *' sort which had then appeared ? And could it bie possible that 

 " he had forgot, what he has himself said of it, in his Etrennes 

 " Chronometrujites for the yenT 17591 I thall now set his own 

 *' words before him." "Convinced" (said he) '* of the verity of 

 " the sentiment of Deicar^ffi, I undertook, in 1751, to make 

 " a clock to go eight days with one wheel only in the movement. 

 " What gave me the idea of this construction, was the 'scape- 

 " ment of a watch with a rest or dead-beat, and a detent, 

 '^ which I presented to the Academy in the year 1748, with 

 " whom it carried or received a favourable opinion, as may 

 ** be seenjn the Memoirs f( r that year. 3Iy contrktance was 

 " not so nexv as I had mag'ined : M. M. du Tertre''s sons, con- 

 " siderahle artists •« many *-espects, shewed me, soon after, a 

 " model fif the watch of their late father's, and ichich the 

 " eldest M. du Tertre must' still have. This model, though 

 *• very different from my construction, is, however, the same 

 *' as to the end proposed ; the motion in both is only re- 

 " stored to every other vibration, &c. And lower down we 

 " read what follows :" " The liberty or freedom procured to 

 " the regulator in the 'scapement of JNI. du Tertre, by a 

 *' detent formed like a long lever, which was stopped * dur- 

 " ing two vibrations by the arbor of the balances, and 

 " moved by an anchor, seemed to me at that time verv 

 " advantageous, &c." 



" The late M. Camus was not then so very wrong, when 

 " f shewed him, in 1754, my 'scapement having a detent 

 *' and free vibrations, in telling me, that long ago the de- 

 " ceased M. du Tertre had proposed and made use of one 

 " like it. We shall find ourselves, M. L. R. and me, in 



* The description of Du Tertre's 'scapement, as given here by 

 Lc Roy, is unintelligible and obscure. ~ Du Tertre was much en- 

 gaged in improving 'scaperaeats about the year I724v 



"the 



