ipa Oh the Trains ef Cloch and IVatchei. 



and fraflional parts of a vibration are calculable by the general rule for watches &\x(tiAf 

 given. 



I am, fir, with much efteem, your's, Sec. 

 Lincoln, May g, rygg. W.Pearson. 



P. S. Since the preceding part of this article was written, I have met with a train propofed 

 for a new watch to indicate feconds, and quarters of a fecond, by the beat, under the word 

 *' clock," in vol. v. part i, p. 76, of the Encyclopedia Britannica, which, by the mode of 

 expreffion adopted before, will ftand thus : 

 48 great wheel 

 12 60 fecond or centre do. 

 10 60 third do. 

 •j\ turns on the fufee. 6 48 contrate do. 



To go 30 hours. 6 15 crown do. 



2 palettes. 



The reader will perceive that thefe numbers conftitute one of the 108 varieties given 

 above, except that the great wheel is given fmaller here, by reafon of the fufee having more 

 fpirals. Under the fame article, I alfo find that, as I fuppofed, fpring clocks are hot coft- 

 ftruded to flieW feconds, though it has been fhewn that they are capable of many difFdrent 

 conftrudlions, which are equally calculated to aufwer this purpofe, as well as to make, at the 

 fame time, a given number of vibrations in a fecond. 



Likewife, I have juft had an opportunity of examining a fmall lartlm, or alarum clock, 

 going by a fufpended weight, and regulated by a fhort pendulum only 4^ inches long, which, 

 confequently, makes upwards of three vibrations in a fccoiid, and which, I nnderftand, mea- 

 fures time pretty accurately. I mean as accurately as thefe clocks are intended to do ; for 

 great accuracy cannot be expefted from a clock with a very {hort pendulum, particularly if it 

 be a fpring clock that goes a week ; on account of the difficulty of forming the fufee to cor- 

 refpond exaftly to the aftion of a powerful fpring for many fucceffive days, as well as on 

 account of the imperfedtions of the pendulum: but whatever be the error in any day, the 

 error in the time of a beat of that day will be a proportional part thereof; and provided the 

 rate of going he tolerably i^niform throughout each fucceffive day, after winding up, the 

 beats will alfo be nearly uniform : I fliall, therefore, give the numbers proper for the third 

 portion of a train fuitable for a pendulum, to vibrate three times in a fecond, which I had 

 purpofely omitted. If any of the ift or 2d portions, already fpecified, be adopted, the con- 

 trate wheel will be 48, with a pinion of 8, and the crown wheel 15. I have preferred a 

 pinion of 8, from a perfuafion that this number will render the works of a watch or clock 

 more perfect, than either 7 or 6 would do ; and is the number we find in the beft finiflied 

 inftruments. If any perfon fliould wifli to try the adtiOn of a pendulum to fwing the quar- 

 ters of a fecond exaftly, any of the trains propofed for a new watch will be found applicable 

 to this purpofe. I'he reafon why an edd number is always fixed Upon as proper for a crown 

 .wlieel, will need no explanation. 



May nib. II, Obftr- 



