tHRONOMETRY* . 161 



^giire given in Thioiif s work. Mr. Reid saves himself' 



the trouble of referring to the passages of the books he 



quotes in the course of his paper; but, as our object is, 



not only to rectify, but to enable other persort8*"to judge —and has not 



for themselves, we think it inciifnibent upon us to do it quoted his ori- 



forhim; and shall also annex a faithful copy of that 



part of the abovementioned work, fromj^^which he has 



taken the escapement here treated of, bat which he has 



altered into a detached form. 



Fig. 5. Plate 3. is a copy of the representation given Correct cqjy 

 by Thiout (Fig. 30. Plate 43. Vol, I.), and the follow- here^gWcn. '"" 

 ing is a literal translation of his explanation of that me- * 

 chanism (p. 1 10. ditto): '' It is an esca£ement of a watch 

 in which half of the vibrations seem lOTependent of the * * 



train of wheels^ while they are performed. The detent B 

 stops the escape wheel ; the balance bringing back ^he 

 pallet A, the detent recedes, to leave the escape ^vheet 

 free to strike the pallet: and so on. This escapement 

 could not perform without a spiral spring*." 



From the preceding description, it plainly appears Explanation. 

 that this escapement acts with a single pallet, and^ de- ^^^^^^ L^^" 

 tent to stop the train of wheels during the intervals th^t 

 elapse between the successive communications of the main- 

 taining power; but that the balance In^t, is nalrerdi|pn- The detent 

 gaged from the detent ; consequently this construc^on bdJncrduriM 

 does not possess the distinguishing principle of tne de- the repose* of 

 tached escapement. Mr. Reid has made it a very di^ ^^^ wheeh 



ferent thing, by introducing certain alterations, wl^jlh Mr Klid's ait 



will be easily perceived, on comparing his^ure with that »^ered escape- 



of Thiout. He has broken the coSnunication between be^freef"' *^ 



the detent and the pallet, and provided the foAiei^^ a 



fork, which is not in the original ; and the escapement, ^ ^ 



with th^e changes, seems, at first sight, capable of acting 



freely. Such, however, is not the constructiop given by 



* For the reader's satisfaction, as well as our own, we subjoin an 41 



exact copy^fThiout's explanation: " Fig. 30. esfikin echapemeht *' 



de montre dont la moitie des vibrations paroissent independantes du 

 rouage, pendant qu'elles se font. Le crochet B reticnt le rochet; 

 le balancier ramcnant la paletie A, le crochet s'eloignc pour laisscr 

 le rochet libre a frapper la palette; et ainsi de suite. Cctte sorte 

 d'echappement ne sgauroit aller sans spiral." P. no. 



Vol. XV.-^OcT. 1806. Y Thiout: 



