PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 857 



verse pipe for steam is connected, alike common to all sections. 

 The whole being set up in brick work, with proper sta}^ bars and 

 braces, forms a compact and exceedingly neat structure, occupying 

 much less space than ordinary boilers of like capacity. By such 

 a combined arrangement it is only necessary to multiply the num- 

 ber of sections to increase the duty of the boiler to whatever extent 

 of power may be required. 



A sphere of the Harrison boiler holds about a gallon of water, 

 and an ordinary section, itself a boiler, is composed of seventy-six 

 globes, tifty-cight of which are filled with water, the remainder 

 being for steam. 



Facility for Enlargement and Transportation. 

 The construction admits of the boiler being enlarged at will, 

 from a small to a larger generator of steam, and such addition is 

 made without disturbinij:; the walls or the floor of the building: to 

 receive it. It also admits of beinc; combined, accordino- to the 

 capacity or the shape of the place it is to occupy. Dissected, it 

 may be conveyed through anj^ ordinary door or stairway, a facility 

 greatly in its favor; also for its transportation, particularly across 

 country and over hills and mountains remote from water or rail- 

 road facilities of travel. 



Strength of the Spheres. 



These globes are capable of sustaining a steam pressure of more 

 than 1,000 pounds per square inch. Mr. Zerah Colburn, then 

 editor of that sterling journal of practical science " The Engineer," 

 published in London, and now editor there of another celebrated 

 scientific journal, "Engineering," in a treatise on steam boilers, 

 read before the British Association for the Advancement of Science, 

 in speaking of this boiler, said: " The bursting strength of these 

 spheres corresponds to a pressure of upwards of 1,500 pounds per 

 square inch, as verified by repeated experiments, being therefore 

 from six to seven times greater than that of ordinary Lancashire 

 boilers of large size."* 



It will be seen that each sphere is a boiler in itself, of great 



* Mr. Harrison being in England in 1864, had some boilers made there upon this system, 

 chiefly to test its practicability. The arrangement of the spheres has been greatly modi- 

 fied and improved since his establishment in Philadelphia or works specially for the con- 

 struction of this boiler. Mr. Colburn, whom I shall have several occasions to quote in this 

 paper, fully investigated this boiler and its operations, and regarded it as a complete suc- 

 ees8. 



