374 INVENTION OP THE BALANCE SPRI?fG. 



Account of the ^' ferent degrees of force of the same spiral, accordingly as it is 



SrenURoy " »^^^^ ^r hss bent up." 



and Berthoud " The experiments which I pointed out are pretty dearly 



tfm^piece^ " designed ; so much so, that they might assist artists 

 " who know how to make use of materials when set before 

 " them. T/ie duration of the great and of the small arcs of 

 *' vibration of the free balance, and the different degrees of 

 " force of the same spiral accordivgly as it is more or less bent 

 " vp. Here is the origin of my theory on the isochronism of 

 *' the vibrations by the spiral. 1 had no occasion to make 

 " use cf it, when I wrote the first part of my Essai sur 

 " rHorlogerie, because the oscillations of the regulator, in 

 *' my first marine clock, were necessarily isochrone, from the 

 " construction of the machine ; first, because the 'scapenvent 

 •* corrected the inequality of the time or duration of the great 

 '* and small vibrations, which might result from changes in the 

 " motive force, from variations of friction, and from the thick- 

 " ening of the oil, &c. (Essai, No..21 iC) ; secondly, because 

 *' the regulator being composed of two balances, the agitation 

 " of the ship could not change the extent of the arcs of vibra- 

 " tion, (see Essai, No. 2097). Thus, in all cases, the dura- 

 " tion of the great or small vibrations must be equal, whether 

 " by the assistance of the 'scapement, or by the nature of the 

 *' regulator. But since I had suppressed one of the ba- 

 ** lances, it became necessary to seek to correct the inequalities 

 " of vibrations, which might result from the agitation of the 

 " ship, and which were corrected by the double balance ir? 

 " the first construction. I came back then to my original 

 " ideas, and sought to correct by the spiral the alteration 

 " which the agitations of the ship might produce on the extent 

 " of the arcs, and on the inequality of the vibrations. Such 

 " is the origin of my theory of the spiral : a theory which is 

 " my own, as is obvious, and very easy to see ; and I do not 

 " dispute with M. L. R. his having made the discovery on 

 *' his part also. We must remark, however, an essential 

 *' difference between the importance which he attaches to 

 " the property which the spiral spring has, of rendering the 

 " vibrations isochrone, and the utility of which I have thought 

 " that this property might be. Tt is chief y on the isochronism by 



" tJ-e 



