OP ARTS AND SCIENCES. 391 



'' It would not be proper to give a detailed description of the struct- 

 ure, because there are patents on certain portions of it that are not 

 yet secured ; but a general sketch of it is admissible. 



"This testing machine was ordered in June, 1875, by the United 

 States Board on the Testing of Iron and Steel, of which Colonel T. T. 

 S. Laidley, U. S. A., was chairman. It was completed about three 

 years ago. The first patent was in 1872, and others have since been 

 granted or are now pending. The machine has as its source of pres- 

 sure a hydraulic accumulator ; and by this pressure the specimen is 

 held in place, and a steady and easily controlled strain is imparted to 

 it through a hydraulic press. 



'' This straining press has a double action, which, in connection with 

 the alternating bed and platform of the scale, allows a test, either by 

 compression or tension, without the addition of intervening parts. 

 The strain upon the specimen is transmitted directly and without fric- 

 tion to liqiud supports capable of receiving a strain of 1,000,000 

 pounds, without exceeding the safe limit of strain for diaphragms 

 intended for perpetual use. 



" The pressure in these liquid supports is communicated, without loss 

 and with great sensitiveness, to other supporting chambers acting 

 directly, and still without friction, through a single pair of levers 

 having steel-plate fulcrums. These last, as distinguished from knife- 

 edge fulcrums, are not subject to injury from load or shock; may be 

 protected from corrosion ; allow a free movement of the beam ; may 

 be adjusted exactly ; and are durable, since their motion is molecular 

 and far within the limits of elasticity. By means of similar fulcrums, 

 the strain — now reduced — is communicated to the scale beam, and 

 motion is imparted to the indicator rod, where a variation of a single 

 pound is distinctly visible, if the load be small ; and for the maximum 

 load of 1,000,000 pounds, a variation of ^^o.Vtjtjj ^^ ^^^^ pounds, may 

 be noted ; while by an admirable system of levers the total weight is 

 recorded on an indicator plate. The specimen tested may even be 

 thirty feet in length, — a limit which would include many built-up 

 structures, such as columns, trusses, and bridge spans. 



"Among the proof experiments to which this machine was subjected 

 by the United States Board, the following may be quoted : — 



" 1. A forged link of hard wrought iron, five inches in diameter 

 between the eyes, was slowly strained in tension, and broke short off 

 with a loud report at 722,800 pounds. 



" 2. In order to see if the weighing parts had been disturbed by the 



