122 



ON THE POWER OF FLUIDS IN MOTION TO PRODUCE 



I shall conclude these remarks with illustrations derived from two obvious 

 and simple experiments. 



Thus an examination of the relative power which different filaments possess 

 in resisting instantaneous and. accumulative loads may be conducted as fol- 

 lows : — 



Suspend from" a thread (m) of the substance examined, a weight (a) that is 

 insufficient to cause rupture: let a weight {a) exceedingly nearly equal to 



Fz^y- 3. 



{a) support the latter through the medium afforded by the fine 

 thread [n) that passes over the very delicate pulley (J). In this 

 state of things it is evident that (m) will merely sustain such 

 tension as suffices to draw it into a rectilinear position; or, in 

 other words, to bring it into the state where elasticity begins to 

 be exerted. Now, by the rapid lateral motion of some sharp 

 edge, as that of a razor, divide {n); and thus transfer, instanta- 

 "^^^ neously, the whole tension of (a) upon the thread {m). The 

 load, in this case, is that -which we have termed instantaneous, and, in conse- 

 quence, rupture will take place under the action of a weight considerably less 

 than if the pressure had been made accumulative, as, by gradually raising («') 

 until (m) had obtained the deflection of load. In the instance of a thread ot 

 fine cotton, the proportion of the weights that caused rupture in the two cases 

 was as 1 to 3'. 



Experiments on the restricted vibrations which 

 we termed explosive, and which last occupied our 

 attention, may be conducted by means of the 

 very case that we chose for investigating the 

 theory of such forces. A massive body (m'), sus- 

 pended by a thread of considerable length, and 

 allowed to rest in its state of equilibrium against 

 . the elastic rod that is to be broken, will supply 

 both the mass (w^') of the theory, and the weak 

 and nearly constant force that urged it; whilst 

 the smaller mass (w), set into motion by suddenly 

 cutting the cord (c), will continue to press against 

 {a) until the spring {h) has nearly attained its 

 point of repose, when, no longer supported by 



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JFcff, 4!. 



