lO 



Stromeyer, Explosions of Steam Pipes. 



wave takes to travel from one end of the bar to the other 

 and back aejain. In the above case 



/ = 



2 . Z _ 2 feet 

 W 17,000 



,500 



second. 



03 



The duration of the blow is therefore independent of the 



velocity of the moving object. 



We can now enquire into Dr. Hopkinson's three 

 experiments. His wires were sus- 

 pended from a beam (see Fig: 7), 

 their tenacity appearing to have been 

 54,400 lbs. and 80,000 lbs. He as- 

 sumed the modulus of elasticity to 

 be 25 millions, whereas 30 millions 

 is probably more correct for iron and 

 steel. Weights of 56 lbs. and 61 lbs. 

 were attached to the bottom of each 

 wire, and, at some little distance 

 above, a clamp weighing i lb. 10 oz. 

 (no details were given in the first 

 experiment) was firmly attached to 

 each wire. Weights of 7, 16, 28, and 

 41 lbs. were dropped on this clamp 

 from various heights. A velocity V 

 would be imparted to the clamp, pro- 



^^^ ducing a pull, P = E-j, both above 



^MJ and below the clamp; the upper pull 



i \ would travel to the point of suspen- 



1 ^^ \ sion and would be reflected down- 



■ ^ wards ; at this point, therefore, and as 



far as the return wave has travelled, the pull would be 



twice as great as at the clamp. If, therefore, P was 



just not intense enough to tear the wire near the clamp, 



J-i- 7 



