INVENTION OF THE BALANCE SPRING, 375 



" Che spiral, that M. L. R, founds, as he tells us, the just- Account of the 

 ** ness of his marine watches ; whilst \ have never considered betweelj.eRoy 

 *' this property of the spring but as an useful accessary ; and Berthoud 

 " and the justness of my mannc clocks depends so httle on^fm^p^^J^^ 

 ** it, that my clock. No. 8, whose spiial was not isochrone, 

 ** has however succeeded very well in two trials of a year 

 *• each. 



** But I will suppose that I had not announced, in my 

 '*_ Essm^ the experiments which have led me to the disco- 

 ** very in question; at least, M. L. R. will not deny that, 

 ** the. lOfk of Februan/, J76S, I deposited, or lodged with 

 *'' tlie Academy, my nexD theory of the spiral, in which I deduc- 

 ** ed this proposition : the oscillations of any balance xiohatever 

 ** may be rendered isochrone by the spiral. Nor can he deny 

 " that the publication of his Expose Succinct was posterior 

 " to the date of eiy deposit ; he would not then be well 

 ** founded, to say that I have borrowed this theory from 

 *' him, or the idea of the discovery, when even, as he falsely 

 *' pretends, this discovery had even been divulged in his 

 *^ .Expose Succinct. But where do we find ii divulged iheva^ 

 ** How has he announced it there? Here is all that he 

 " says of it (page 27 of the Expose Succinct):" " I have 

 *\ discovered a property in the spring, by means of which 

 *' I can easily come at the most perfect isochronism." 



-." What could these enigmatical words teach me ? What 

 ** is this spring? What is this property? We find, at the 

 ** end of the Expose Succinct, a copy of his project of 1754, 

 " in which he likewise said, that his balance would be sus^- 

 " pended by a straight regulating spring, whose property 

 ** was to render all the vibrations isochrone. Is it still 

 *' about a straight regulating spring which JN'I, L. R, would 

 *' speak of in 1768 ? — or of a spiral spring? And I 

 " ask it of himself: Who could divine that these vague 

 " words, a property in the spring, announced a certain 

 " length in the spiral spring ? But again, even if he should 

 " have announced his discovery clearly in the Expose Sue- 

 *' cinct, as he has lately done it in 1770, in his memorial 

 " on the Measure of Time at Sea ; could I ever be sus- 

 " pected of having copied M, L. R. when I had deposited 



" my 



