TIMEKEEPERS, 7;;^ 



cbntinuiug for a certain numcer of degreep, is again return- Description 

 ed by the balance spring from r to S, when resuming its si- ^^^'^ d^atohe^f 

 tuation, it is prepared to act as before. escapement a^ 



It may be proper to remark that the action of the cycloi- "'"stmcted by 

 dal tooth upon the impelling pallat is always the same, in 

 the beginning as in Fig. 6, in the middle as in Fig. 7, and 

 at the end as in Fig. 8, impelling the pallat with the same 

 quantity of surface in action at all times, and at all times 

 equidistant from the axis of the pallat. This however de- 

 pends upon the tooth having the true figure. 



The proper shape of the cycloid is found in the following 

 manner. Having a plate of smooth metal, fix upon it a 

 piece of brass the size of the intended escapemeirt wheels 

 which call the false wheel. Then take anotjier piece of 

 brass the size of the intended pallat, which call the false 

 pallat. On the circumference of the false pallat fix a fine 

 steel point, and then rolling the false pallat upon the cir- 

 cumference of the false wheel, the steel point will describe 

 a line on the plate, which will be the proper curve, in 

 which shape the tooth must be cut by an engine. The 

 larger the pallat in proportion to the escapement wheel, the 

 less sudden the cycloidal curve will be, and the smaller the 

 pallat the more sadden ; so that an escapement wheel which 

 has 15 teeth, with a pallat of a proportionable diameter, will 

 have its teeth of a very different shape to those in a wheel 

 which has only 12 teeth, because, in one case, the pallat is 

 half the size, and in the other it is little more than one 

 third. 



The size of the pallat dependi? upon the number of teeth 

 in the escapement wheel. The radius of the pallat should 

 be equal to the distance between any two teeth of the wheel, 

 and then their relative motion will be equal. If the wheel 

 has twelve teeth, the radius of the pallat wilt be thirty de- 

 grees, measured on the diameter of the wheel, and its dia- 

 meter sixty degrees, measured in the same manner, which 

 will make it half the size of the wheel. If it has thirteen 

 tfi^eth the pallat v/ill in diameter measure fifty-five degrees 

 and a half, if fourteen teeth, fifty-one degree* and a half, 

 and if fifteen teeth, which is the number generally applied 

 to pocket tune-keepers, it will be forty-eight degrees. 



The Marine Timekeeper, which has been here described, Quickness of 



-* Vol. XIV.-^Mav, 1S00\ L is l^" V"'" "^^^'^ 



tunekeepcrs 



