192 



fracture, the ratio of the effect of instantaneous and accumulative ac- 

 tion will vary with the nature of the .substance, never being less, for 

 elastic bodies, than 2 to 1, nor for flexible than 4 to 1, and more 

 usually approaching 3 or 4 to 1 for the former case, and 5 or to 1 

 for the latter. 



5. Let a vase or conduit be acted upon by a load which is alone 

 sufficient to break it, and let this load be partly balanced by a small 

 exterior force : should the great interior force suddenly cease, the 

 small exterior action may crush the vase or conduit inward ; its ener- 

 gy in such case being the sum of the interior and exterior forces. 



6. Should the interior force be a vibration of the kind already ex- 

 plained, and should the exterior action be extremely feeble, and act 

 on a very great mass, this extremely feeble action may crush the 

 vase inward, with a power that shall exceed in any degree the enor- 

 mous action of the interior or explosive vibration. The comparison 

 of the interior and exterior actions is best effected in this case, by 

 finding the modulus of elasticity of a material spring that shall coin- 

 cide most nearly in effect with the interior tremor. For putting e and 

 e' respectively for the modulus of the spring and of the support, and 

 a- and t for the deflections resulting from the tremor acting alone, 



and the reaction as it does act, we have — = * /— , or, in other 



o- yl e 



words, the deflection produced by the reaction, is to the deflection 



that would be produced by the interior tremor alone, in the inverse 



proportion of the square roots of the moduli of tremor and support. 



7. Combining what is here said with the known laws of fluids 

 moving in pipes, and whereby they necessarily produce hydraulic 

 shocks, it follows, that any vessel connected with such a train of 

 pipes, and plunged at some little depth in a considerable mass of wa- 

 ter, or other heavy fluid, will occasionally be subject to a crushing 

 and exterior force vastly greater than the interior strain due to the 

 constant head of fluid. 



In illustration of the principles thus developed, Mr. Bonny castle 

 details some experiments, and mentions a phenomenon which oc- 

 curred under his own notice, and is analogous to the one described 

 by Dr. Hare. In making experiments on the propagation of sound 

 through water, he had occasion to cause an explosion of gunpowder 

 within a hollow metallic cylinder, open at the lower end, and im- 

 mersed under the liquid ; and, although the strength of the cylinder 



