1875.] 00± [Sellers. 



right-angles to these viniting necks in the form of half necks with rebate 

 joints to match with similar joints on the other groups. A group of four 

 balls might be called a unit, and a pair of balls a half unit, corresponding 

 with whole bricks and half bricks in building usage. Each of these units 

 would possess a strength measured by the strength of each individual 

 ball or sphere formmg part of the unit, and a boiler structure built up in 

 any form and to any extent would have a strength identical with the 

 strength of each unit used in its construction. As the various groups of 

 balls were to be held together by bolts passing through the opening from 

 end to end of the pile, it was presumed that these bolts would stretch 

 under an unusual strain and thus permit a leak at the joint, so, making, 

 as it were, a great many safety-valves to relieve the strain. It was of 

 primary importance that the walls forming all the sides of these groups 

 of balls should be of uniform thickness. To accomplish this resu.t a 

 knowledge of the' founding art would be needed. When Mr. Harrison 

 presented this idea to the public he had evidently carefully considered 

 all the difficulties that would occur in the practical realization of it and 

 in its introduction. He had already perfected his plans and was prepared 

 to direct the preparation of the pattei^ns from which these groups of 

 spheres could be cast of uniform thickness of metal, on what is techni- 

 cally known as a green-sand core, so that the first group or unit cast 

 was perfect in all respects. He had also matured a plan of dressing the 

 rebate-joints in the groups by machinery, thus insuring accuracy of size 

 and making the parts interchangeable, without depending on the skill of 

 the workman. 



The first boiler built on this plan was tried in the establishment of 

 Messrs. William Sellers & Co., in this city. It was erected in the spring 

 of 1859, and for many months supplied all the steam needed in that 

 establishment. To avoid all risk from so novel an experiment the cast 

 iron boiler was worked for several months at Mr. Harrison's own expense, 

 fires being kept under the wrought iron boilers in readiness for use should 

 the new one give out . It may be well to mention that from that time to 

 the present writing, these boilers have been in constant use in the same 

 place under some of the many forms afterwards designed. The invention 

 of this kind of safety boiler marked a distinct era in boiler construction ; 

 and whatever may be the ultimate history of this invention, whether its 

 use be continued in future, or it be superseded by other forms, it is 

 nevertheless a well-established fact that its inception preluded all the 

 forms of sectional safety boilers now in use which are presented, each 

 with some special claim for efficiency, durability and safety. Mr. Harri- 

 son did not claim for his invention diminished first cost, nor did he antici- 

 pate any greater efficiency than was obtainable by any first-class boiler, 

 but he was sure of a greater safety in the use of high-pressure steam and 

 he thought that the use of his invention might render possible the safe 

 employment of higher pressures, if desirable, than was before considered 

 possible with any of the ordinary types of wrought iron boilers. 



