HOROLOGY. 



the other, and only differs from it, in be- 

 ing stopped by the inside of the head of 

 the adjusting- screw, instead of the extre- 

 mity of the screw itself, and unlocking 

 outwards and not towards the centre. 



The two constructions, which may be 

 considered as the same, differ from the 

 French detached escapements, such as 

 those of F. Berthoud, which we have al- 

 ready explained in the detent. In the 

 new detent, the pivots are abolished, and 

 the centre of motion is established in the 

 locking piece itself; which, for that pur- 

 pose, is made flexible near the extremity 

 by which it is fixed. The elasticity of the 

 detent, or locking piece, supplies also the 

 office of a strait auxiliary spring, placed 

 behind the lever of the detent, or a spiral 

 spring, which has been sometimes applied 

 to the axis of the pivots, to keep the de- 

 tentin the proper situation. 



The pivots of the old detent are so 

 slender, that its performance cannot be 

 supposed subject to any considerable de- 

 gree of friction ; and watches, with that 

 kind of detent, have been known to go ve- 

 ry well. Some able artists, upon that ac- 

 count, think that the new detent is only 

 preferable to the other, because it saves 

 work and is less expensive ; but while 

 the spring detent is allowed to perform 

 as well, if not better, than the detent 

 with pivots, which its universal use in this 

 country seems to prove, that property, 

 combined with the economy in the manu- 

 factory, must secure to the mechanism in 

 question the character of an improve- 

 ment in the construction of time-keepers. 



To whom are we indebted for the in- 

 vention of the spring'detent ? The general 

 opinion attributes it to the late Mr. Ar- 

 nold ; and we do not see any reason of 

 sufficient weight to refuse him that merit. 

 Mr. Earnshaw has claimed it in his own 

 favour; but Mr Arnold's labours have, 

 at least, the advantage of priority ; and 

 the strength of this advantage not having 

 been done away by any proofs, which in 

 our opinion can be esteemed satisfactory, 

 must decide our judgment in the present 

 case, as in the like controversies upon 

 other points, which have been considered 

 in the course of this inquiry. The con- 

 trivance of the locking spring, or spring 

 detent, therefore, appears to us to be due 

 to the late Mr. Arnold. With regard to 

 this mechanism, it is also worthy of re- 

 mark, that the invention is entirely Eng- 

 lish, not a single passage existing' in the 

 writings of the French authors, by which 

 any one of them might claim it with rea- 

 son, or even plausibility. The first men- 



tion of any thing like the locking spring, 

 to be found in foreign publications, is the 

 detent without pivots, given by F. Ber- 

 thoud in his " Supplement au Traite des 

 Horloges Marines;" but that book was 

 published in 1787, that is, five year* after 

 Mr. Arnold had taken out his patent, and 

 \yhen many watches upon that construc- 

 tion had been in circulation. We eannot, 

 therefore, allow him the credit of this 

 thought; nordo we find that other French 

 artists have availed themselves of that 

 hint, to carry the spring detent to the 

 great degree of simplicity which it has 

 attained in this country. 



A little afterthe invention of the detach- 

 ed escapement, the isochronism of the vi- 

 brations of the balance, by means of the 

 spiral spring, was, if not newly discover- 

 ed, at least perfected and brought into ge- 

 neral notice, and that principle added a 

 great value to the detached escapement, 

 while this mechanism secured the utility 

 of the principle, by offering the species of 

 insulated balance which it required. From 

 some theories and experiments long 

 known to the world, it would appear that 

 the vibration of a spring might be always 

 supposed of equal duration ; and that ad- 

 vantage Dr. Hooke asserted himself to 

 have attained with his invention in watch- 

 es, which had been shown to several per- 

 sons. The principle, however, could not 

 be generally trusted, according to Dr. 

 Hooke himself, who, in the postscript to 

 his description of Helioscopes, (p. 29,) de- 

 clares, that he had explained how the vi- 

 brations might be so regulated, as to make 

 their durations, either all equal, or the 

 greater, slower, or quicker, than the less, 

 and that in any proportion assigned. We 

 must suspect that these ideas were not 

 properly digested, or regret that their 

 communication by the author, in his lec- 

 tures in Gresham College, was not suffici- 

 ently explicitto give precise rulesfor prac- 

 tice, and fix the attention of watch-makers 

 upon the subject. After those hints, the 

 principle seems to have been very little at- 

 tended to for many years, and the isochro- 

 nism was frequently attempted to be ef- 

 fected by means of mechanical contriv- 

 ances in the escapement. Harrison endea 

 voured to accomplish that important ob- 

 ject, by the form of the back of the pallets . 

 and on the return of the voyage to Jamaica, 

 added for the same purpose the cycloklai 

 pin, to regulate the balance spring; but 

 this method of adjustment never ap- 

 peared satisfactory or certain. P. le Roy, 

 in his " Memoire sur la meillure Maniere 

 de mesurerle Temps en Mer," rev/rded 



