6'i 



Ttie measnrJnG 



TIMKKKEPERS. 



VII. 



Explanation of Timekeepers, consintcted hij the late Mr, 

 John Arnold ; for ichich a Rczcard of £3000 ivas given 

 hi/ fife Board of Longitude to his Son Mr. J. R. Arnold, 

 Extracted from the Account delivered by the latter to the 

 Commissiuncn.* 



CONSIDER the chronometrical part of the tiraekeeper to 



capument 



tlic oaiaecc on 

 its spring-. 



jiartsinatime- be confined altogether to the balance spring, the balance, 

 i'ahnf^t' spi'in?, ^"^ ^^^^ escapement. The' other parts are no more than a 

 le lialiiiic", good horizontal movement, which may be of any dimen- 

 sions from two inches and a half in diameter, to five or 

 more, and of proportionable depth, and may be constructed 

 to go a day, a week, a month, or even a year (though 

 the last may not be quits so well) at the option of the 

 maker, 

 Sw^pension of [About three pages next following are employed on a 

 description of the train and construction of the box time- 

 keeper ; in which there is no singularity asserted, except 

 that the spring of the balance, which is helical, is made to 

 exert a power endways or edgewise, to such a degree, as very 

 nearly to support the weight of the balance v.hen quiescent, 

 and actually to cause its upper pivot to press against the 

 potence, when the re-action of the spring is near its maxi- 

 mum. By this means, as the writer observes, a considerable 

 degree of friction is avoided.] 



Of the Balance Spring, uifh the Mode of rendering it Isochro- 

 nal, or of adjusting the long and short Arcs of IlbraNon of 

 the Balance. The Terms long Arcs, and short Arcs, large 

 Arcs, and small Arcs, arc used indiffereiitlij. 



B.'ilftnce The balance spring may be made of steel wire hardened 



sprini^: le ica , ^,.j,| {(.j-j-jngi-^^j of gj-ppi ^ff'\xft hard rolled, or of gold wire alloy- 

 so'tij ed with copper. Steel wire hardened and tempered is the 



■f Dated March 5, 1805. Tlic words of the writer are relaincd? 

 and the paper no otherwise shortened than by omitting wIiuL re- 

 fers to the movcimml. Av 



mo.it 



