OP ARTS AND SCIENCES : JANUARY 9, 1872. 339 



destructive explosions of plate-iron boilers, and, to use the words of 

 the report, " that in accounting for either the fact of an explosion, or 

 for its destructive effects, there is no necessity for hypothesis of low 

 water, enormous pressures, instantaneous generation of immense quan- 

 tities of steam, superheated steam, the formation of hypothetical gases, 

 the development of electricity, &c, &c. The most frightful catastrophe 

 can be produced by simply gradually accumulating the pressure of the 

 saturated steam to a strain, at which the strength of the boiler yields, 

 nor need that pressure be much above what is ordinarily employed 

 with boilers of this type." In one experiment the boiler exploded 

 with most destructive violence in less than a quarter of an hour after 

 the pressure had passed the inspector's limit. 



Such a sudden tearing open of the whole vessel has never taken 

 place, and does not seem to be possible, with the Harrison boiler. Un- 

 der an excessive pressure the weakest units in the system may yield, 

 and injury may be caused by the sudden discharge of water, or of 

 steam ; but the injury to the boiler must be, to a great extent, local, 

 probably extending only to the breaking of a single unit, and involving, 

 at the most, a rapid but still regulated emptying of its contents. The 

 parts being wholly independent, there is no tendency in a rupture to 

 extend from one unit to its neighbor's ; and moreover, as a general 

 rule, long before the bursting-point is reached, a third feature of the 

 boiler comes into play, which, perhaps, more than either of the other 

 two, protects it from destructive explosions. The units of the boiler 

 no^ being cemented together, the least yielding of the tie-bolts opens 

 every joint and makes each of them a safety-valve. That this is the 

 normal action of the boiler under excessive pressure has been abun- 

 dantly established, not only by the experiments made by Mr. Harrison 

 before a committee of the Franklin Institute, but also by the experi- 

 ence of a member of our own committee. 



The Rumford Committee were satisfied, by the evidence herein 

 stated, that the Harrison boiler is not liable to those violent destructive 

 explosions referred to above, and to which the ordinary plate-iron 

 boilers, however carefully or strongly made, must be always more or 

 less exposed. Considering further the economical advantages to be 

 gained from high-pressure steam, and the paramount importance of 

 such security as Mr. Harrison has attained in the use of this powerful 

 agent, they felt themselves justified in making the recommendation, on 

 which the Academy acted, in awarding to him the Rumford medal. It 



