340 PKOCEEDINGS OF THE AMERICAN ACADEMY 



must be noticed, however, that the award has been made for a " mode 

 of constructing steam-boilers, by which great safety is secured" and 

 that the safety of the boiler is the only point on which the committee 

 based their recommendation. They did not feel themselves called 

 upon to weigh carefully the relative merits of the Harrison boiler when 

 compared in other respects with the many forms of steam-boilers now 

 in use. They considered that its already extended and rapidly increas- 

 ing use was sufficient evidence that the Harrison boiler was an efficient 

 and economical steam-generator. More than this they did not require 

 to be proved; for whatever might be the defects of the boiler, — and 

 some doubtless there are, — the committee considered that Mr. Harri- 

 son had made an important advance in the application of steam by 

 demonstrating experimentally the principles on which a safe steam- 

 boiler can be made, and working them out to a practical result. 

 These principles being established, we may hope that any defects in 

 the present construction may be hereafter remedied. 



It remains only to consider how far the principles or features of con- 

 struction to which we have referred are original with Mr. Harrison. 

 At least twenty-five years ago Dr. Ernst Alban, a distinguished Ger- 

 man engineer, clearly recognizing the impossibility of securing safety 

 in a steam-boiler by strength of materials alone, advanced the impor- 

 tant opinion that the only sure method of avoiding danger is " so to 

 construct the boiler that its explosions may not be dangerous " ; and 

 in a valuable work originally published in Germany, but of which 

 an English translation, published in 1843, was alone before the 

 committee, a mode of constructing steam-boilers is described in 

 which this principle is skilfully applied. Mr. Harrison has adopted 

 the principle of Dr. Alban, and, in a pamphlet on the steam-boiler, 

 published at Philadelphia in 1867, he prints the opinion of Alban, 

 quoted above, at the head of his essay ; but his method of embodying 

 this principle is as dissimilar as possible. Moreover, he has carried 

 out the principle more fully than Alban himself. The German boiler, 

 like the American, is made in sections, so that the bursting of one would 

 bring no destructive consequences from the general body of the boiler ; 

 but it is merely a modification of the well-known tubular boiler, and 

 does not -combine the advantages which Harrison obtains from the 

 spherical form of his units, and the mode by which they are bolted to- 

 gether without rivets or cement. 



Rut the merit of Mr. Harrison and his claim to the Rumford medal 



