1 88 Master Minds of Modern Science 



it is to test railway couplings. It is known as an impact- 

 testing machine, and the blow it delivers corresponds to 

 dropping a mass of one ton through five feet. By re- 

 peatedly dropping a ton weight on to a coupling or a 

 chain it is possible to discover the precise strain or stress 

 which it will stand in actual use. The railway companies 

 adopt only the designs which have proved themselves able 

 to stand a strain many times greater than any they are 

 likely to endure on the line. Thus the public is safe- 

 guarded. 



The Laboratory has several machines for doing damage 

 to metals. In fact, some of its scientists are at work all 

 day smashing up pieces of metal that have been made 

 with great care. One machine stretches steel rods to dis- 

 cover how great a strain they will withstand before 

 breaking, another squeezes metals, a third twists them, 

 and yet another bends steel springs backward and for- 

 ward about a thousand times a minute for hours on 

 end, all the time automatically counting the number of 

 times the spring bends. Finally the machine shows the 

 number of times the spring can be bent before it gives 

 way. This type of experiment has proved valuable in 

 testing the springs of motor-cars ; and the springs on the 

 car or bus in which you ride are better and safer than 

 they would be were it not for this work. 



These experiments are linked up with the very im- 

 portant question of ' fatigue ' in metals. 



Now that industry is constantly building machines for 

 working at terrific speeds under high pressures, engineers 

 must know how much strain a metal will stand. 



Occasionally we hear that the steel arm of a crane has 

 cracked, perhaps causing loss of life. After an event such 

 as this the maker of the crane will send a sample of the 

 metal to the Laboratory for testing, and the experts will 

 tell him why the metal failed. 



Testing the hardness of a metal is really quite a simple 



