496 PROCEEDINGS OF THE AMERICAN ACADEMY 



of 144 revolutions per minute. Its position is horizontal, and at a level 

 of 3 feet below the surface of Merrimack River at its ordinary stage. 

 It is mounted upon a vertical wrought-iron shaft 25 feet long and 6 

 inches diameter at smallest place. This shaft is fitted at its upper end 

 vpith a series of disks, by means of which it is supported in its box, 

 which again is supported by a massive cast-iron frame. This frame 

 supports the entire weight of the wheel and shaft. The shaft at its 

 lower end is bored in the line of its axis to a depth of 5^ inches to re- 

 ceive a steel pin of 17j- inches length and 2J- inches diameter ; and 

 which projects from the shaft 12 inches. The steady-pin has no func- 

 tion to perform other than that of restraining the shaft from lateral 

 aberration. It is free to revolve in a box made of three pieces of case- 

 hardened iron, so placed in a cast-iron frame as to allow free play to 

 the steady-pin and the free access of water to it. Each of these three 

 pieces composing this box is kept up to its place by following-screws 

 working in the cast-iron frame which is bolted to the stone floor of the 

 turbine pit. In the Tremont turbine this floor is of wood, and in Plate 

 I. the steady-pin is marked 'I.' 



" The pieces sent are marked Nos. 1 to 5. No. 1 is the portion of 

 the steady-pin which was nearest the shaft ; No. 2, the other extremity 

 of the same pin ; Nos. 3, 4, 5, the three pieces of case-hardened iron 

 forming the box, with portions of the steady-pin attached. You will 

 at once perceive that this steel has been partially fused, and can thus 

 account for its attachment to the iron. 



" The facts are, that on noticing some irregularities of motion on the 

 part of the wheel, it was stopped, and the water pumped from the pit 

 until the floor was bare. Inspection showed that the following-screws 

 had not done their duty uniformly ; and the three pieces, Nos. 3, 4, 5, 

 no longer preserved their proper relative positions, nor allowed free 

 play to the steady-pin. The consequence was, an amount of friction 

 causing heat sufficient to fuse steel, although the latter was immersed 

 tliree feet deep in a raceway ten feet wide, through which was passing 

 seventy-five cubic feet of water per second. 



" A similar accident happened thrice to our turbines, which are now, 

 however, safely guarded against such mishaps." 



There are two points in connection with these facts to which I 

 wish especially to call attention. In the first place, the weight of the 

 wheel did not rest upon the surfaces of friction. The three pieces of 

 case-hardened iron in their displaced position acted simply as a brake 



