552 Prof. Trouton and Mr. Rankine: Stretching and 
breaking the contact may occur for very small changes 
ot length. The temperature effect was eliminated by the 
use ‘of the plate suspended by lead wires, as in the previous 
experiments. 
Fig. 10. 
Now let H and F be not in contact, the pull on the wire 
stretches A until they come into contact. As soon as this is 
the case, the first relay R, is brought into action, and this in 
turn causes relay R, to act. A current flows in the electro- 
magnet D, and the knife-edge K is raised one or two milli- 
metres. Now K has been pressing on a piece of rubber 
tubing and preventing water from syphoning from B. When 
it is raised, water runs off from B, and E rises, breaking 
contact. Immediately the weight L pulls K down into its 
former position, and water ceases to flow. The intermittent 
action of the valve K causes E to be always just on the point 
of contact with F. In other words, the wire A except for 
temperature effects remains the same length throughout. 
To record the way in which the water comes off, it is run 
into a second vessel T, which is suspended from the spiral 
spring 8. <A lever is fixed to the spring at M and turns over 
