Polytechnic Assoctatiox. (387 



the pressure, no explosion can ever occur. We doubt the truth of 

 this theory to the extent asserted. 



• "With all imaginable care and unquestionable ability in the engineer, 

 and well constructed boilers of good material, explosions have, never- 

 theless, happened, if any faith is to be accorded to human testimony. 



Although incompetent engineers have sometimes been placed in 

 charge of steam-power, and weak and insufficient boilers have been 

 often in use, yet the explosions are far too numerous and terrible to 

 suppose that they are all owing to the imputed cause of negligence, 

 ignorance or defective boilers. We could as easily believe that all 

 the 700 shipwrecks which take place in the course of a year are owing 

 to want of seamanship in the crews or sea-worthiness in the .vessels 

 cast away. Men engaged in the management of steam-engines are 

 not ignorant, at any rate, of the dangers to which they are exposed, 

 and have a natural regard for their own safety. Few men are utterly 

 reckless of life ; and it is not conceivable, when so much in such 

 situations obviously depends upon care and skill, that any considerable 

 number of engineers should be employed without the requisite 

 qualifications. Therefore, when on the occurrence of many of those 

 explosions the investigation of the facts fails to show either want- of 

 skill and care, or insufficiency of the boiler, we are fain to accept the 

 verdict as it is given, — cause unknown. 



The commonly received explanation, which ascribes the catastrophe 

 to the expansion of steam, is not satisfactory to us for many reasons ; 

 some of which we shall endeavor to present. When first vaporized 

 from water heated to 212 degrees, steam assumes a volume 1,700 

 times greater than that of the water from which it is evolved ; and 

 every added degree of caloric, though it does not raise the temperature 

 of the steam, increases its expansion one 490th part, which is 

 ascertained to be the regular rate of increase of all gases and vapors 

 on the application of augmented heat. The expansion or pressure of 

 steam, therefore, increases by regular gradation, and is measured with 

 perfect accuracy. When the pressure rises to the point, or approaches 

 that point, at which the boiler would give way, a valve is opened, 

 and what is the result ? The steam in the boiler is instantly diminished, 

 and the danger ceases. If there is no such valve, or it is not attended 

 to, and the boiler gives way and opens in some weak part, is it not 

 the proper and natural consequence that the moment the steam finds 

 an issue through the rent, the strain or pressure will be lessened by 

 the escape of the steam, as it is when it escapes through the safety 

 valve ? In estimating the effect of this strain, we must bear in mind 



