96 THE EMERY MACHINE. 



to occur, and repairs are required more frequently 

 When carrying out a test on a simple machine the 

 operator has his mind left free to be fully concentrated on the 

 test he is performing. The simpler a machine the less 

 likely it is to get out of order, and the more easily is any 

 displacement, or anything abnormal, at once seen. 



It is chiefly in the weighing apparatus that variations 

 as to comparative simplicity are to be found. The strain- 

 ing appliances used in this country are nearly always of the 

 hydraulic cylinder and ram type, and there is little real 

 difference in their arrangement. 



In nearly all the English machines the weighing appara- 

 tus consists of a lever, or system of levers. The fewer 

 the levers, the simpler the machine. The loads in the 

 specimens are measured by noting the position on one of 

 these levers, of a weight or weights ; the simpler machines 

 use a single invariable weight, as against a set of several 

 smaller weights in others less simple. 



The two machines which employ single levers are the 

 Werder and the Buckton-Wicksteed. Of these the 

 Werder is prejudiced by the fact that its very small 

 fulcrum distance is the cause of several complications. The 

 Wicksteed single-lever vertical machine is undoubtedly the 

 simplest in all respects. There is only one lever ; the 

 fulcrum distance is not abnormally small ; there is only 

 one travelling weight, the steelyard principle being 

 adopted in its entirety ; and there are only two knife edges 

 to get out of order. One of the great beauties of this 

 machine is due to the fact that the measurement of the load 

 depends on one thing only, namely, the position of a weight 

 of fixed magnitude on a straight horizontal lever. There 

 are no calculations needed in order to ascertain what the 

 load really is ; the value is given direct, and at once. 



In all the compound lever machines the number of 

 knife edges is increased, and the simplicity diminished 

 accordingly. Where variable weights are used, the com- 

 plication is further increased by the fact that in addition 

 to the trouble involved in the changes, the actual loads can 

 only be arrived at by means of calculations. This variable 

 weight question is one upon which experts differ. Professor 

 Kennedy, for instance, prefers to be able to vary his load 

 so that he can accommodate it to the size and material 

 of the specimen he is testing, and thus use approximately 

 the whole range of the scale beam in every case. Much of 

 the complication of testing machines arises from the fact 



