382 NATURAL THEOLOGY. 



c, seven times and a half (for 60 -^- 8 = 7^) during 

 one revolution, or sixty times during the eight rev- 

 olutions which B makes in one hour. 



Thus we have the minute-hand and the second- 

 hand measuring minutes and seconds of time on 

 the dial ; but we have not yet the hand which shall 

 go round in twelve hours and mark the hours on 

 the dial. To effect this the same machinery is 

 used : viz., the wheel and pinion ; but the moving 

 power is applied so as to diminish the rate of mo- 

 tion — that is, by making the force act from the 

 leaves of the pinions to the teeth of the wheels, 

 instead of from the teeth to the leaves. 





36' 



We may remember that the centre wheel, a, 

 goes round once in an hour; that the axle of this 

 wheel passes through the dial and has the minute- 

 hand attached to it. The pinion of this wheel, 

 called the cannon pinion, has ten leaves, which 

 I ay, during the hour, upon a wheel, b, having forty 

 teeth, which, accordingly, is moved round only 

 once in four hours. This wheel, b, has a pinion 

 of twelve leaves working into a wheel of thirty-six 

 teeth, and must therefore make three revolutions 



