Chap. 3.] Force of Exparjion-. 109 



farthing candle was able to lift a weight of five hun- 

 dred pounds, without any afliftance from the mecha- 

 nical powers; and he fhews that the fame infignificant 

 power, namely, the flame of a fmall candle, would by 

 the force of expanfion overcome a weight even of five 

 thoufand pounds, could an inftrument be conveniently 

 fitted up for the experiment*. Indeed, when we 

 confider that the force of cohefion in metals is fb 

 great as to enable a gold wire of one-tenth of an inch 

 diameter to fupport five hundred pounds weight, and 

 an iron wire of the fame dimenfions to fupport one 

 thoufand five hundred pounds, without producing any 

 feparation of the parts ; what mufl be the force of fire, 

 which can relax and even difTolve the texture of the 

 firmeft metals f ? 



It is a fact univerfally known, that clocks and time- 

 pieces in general go flower in warm weather, and falter 

 in cold j this effect is owing entirely to the expanfion 

 of the pendulum, which being lengthened by the ac- 

 ceflion of heat or fire in warm weather, makes a lon- 

 ger vibration, and confequently lofes a proportionate 

 quantity of time ; on the contrary, the length of the 

 pendulum being contracted by cold, the vibrations 

 will be proportionably quicker, though the quantity 

 of time gained or loft in a fingle vibration may be ex- 

 ceedingly trifling; yet as the vibrations are very often 

 repeated, the effect will in a courfe of time be very 

 confiderable. An alteration of one hundred thoufandch 

 part of the time of a fingle vibration, will amount to 

 nearly that of a whole vibration in the courfe of a 

 dayj. 



The cafes are fo numerous in philofophy and the 

 arts, when it is defirable to be informed of the quan- 



* Jones's Phyf. Difij p. 99, ico. $ Ib. p. 98, 



J Ib. p. 98. 



tlty 



