GREENWOOD MACHINE. 79 



is a wheel on the end of each of the four screws, so that 

 by turning the hand wheel the screws are rotated in their 

 bearings. The nuts in which the screws work form part 

 of the second or movable crosshead. By this arrangement 

 of the screws the movable crosshead can be traversed 

 along the bed plate into any desired position, so as to 

 accommodate specimens of varying length. 



The right-hand end of a tension specimen is held by the 

 grips in the movable crosshead ; its left-hand end is held 

 in a small crosshead, which is attached by side links to 

 the first knife edge of the first-motion lever. 



A tension test is carried out as follows : The movable 

 crosshead is first adjusted into a proper position suitable to 

 the length of the bar which is about to be tested. The bar 

 is then placed in the holding grips, the hand wheel turned, 

 and the screws revolved so as to pull the specimen tight. 

 The load on the specimen is now gradually increased. This 

 is effected by moving outwards, in a left-hand direction, the 

 traversing carriage and its pendant weights by means of the 

 small hand wheel and chain shown. As the weight is 

 moved outwards the force upon the knife edge at the end 

 of the short arm of this straight second-motion lever is 

 increased. This force is transmitted directly to the end of 

 the long horizontal arm of the first-motion lever, and this 

 force again is multiplied and transmitted to the specimen 

 from the knife edge at the end of the short, vertical arm 

 of the first-motion lever through the two side links. 



As the load upon the specimen is increased, and elonga- 

 tion begins to take place, the weight lever falls on to its 

 bottom stop, and equilibrium is restored and the strain 

 taken up by admitting a proper quantity of high-pressure 

 water into the straining cylinder. The ram is in this way 

 driven outwards, its crosshead, screws, and the movable 

 crosshead are traversed towards the right and the stretch 

 taken up. 



The water used in the straining C}dinder is supplied in 

 any suitable way, most frequently by hand pumps or from 

 a power-supplied accumulator. 



In the particular machine here illustrated the combined 

 leverage is 112 to 1. The pendant rod carries a number 

 of 50 Ib. weights. There are 19 of these in all, and the 

 carriage and scale plate themselves weigh another 50 Ib. 

 So that when the full number of weights are in use there 

 is a load of 



20x50=10001b. 



