156 



APPENDIX. 

 " arc of vibration of the pendulum, the weight which 

 " keeps it in motion mult be incrcafed, till it is found juft 

 " fufficient to keep the machine going; by which means 

 " there is a certainty that the pendulum vibrates fniiilar 

 *' arcs in each experiment, even if the obferver fhould not 

 *' attend to that circumflance. 



*' The fwing-wheel is made of tempered fteel, and the 

 *' points of its teeth are left much thicker than they 

 " ufually are in clocks, in order to avoid accidents; it 

 " has thirty teeth, and carries with it a divided circle 

 " which fliews feconds. 



*' On the axis of the fwing-wheel there is a pinion, on 

 " which another wheel adls : and in the axis of this lall, 

 " there is a fmall pulley, in the groove of which is applied 

 *' the line which keeps the machine going, by means of 

 " a weight and counter- weight, in the manner defcribed 

 " by Huygens in the eighth and eighteenth pages of his 

 " Horologium ofcillatorhun : this method is the fnnpleft 

 " of any for keeping the wheels in motion while the 

 " weight is winding up, and is peculiarly advantageous 

 *' in fuch machines as this, which require frequent 

 " winding : the weight applied to this machine was fix 

 " ounces Troy, which with a defcent of thirty-two inches 

 " kept it going for three hours, with a vibration of three 

 " degrees. 



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The 



