1912-13.] Error caused by “ Lag” in a Recording Instrument. Ill 
in the running of the turbine, regarded as a water meter, cause it to register 
the total quantity of water in excess or in defect ? We decided first of all 
to take the simplest possible case, namely, that in which the water is 
alternately turned on and shut off for predetermined intervals. To carry 
out the work on its experimental side it is necessary to have an auxiliary 
apparatus which will not only start and stop the delivery of water to the 
A 
? 
Fig. 4. 
turbine ; but which will restart it at full speed. To fully achieve this it is. 
requisite, not to stop the water at all, but merely to divert its flow from the 
wheel at stated times. Accordingly, the apparatus shown diagrammatically 
in fig. 4 was constructed. It may be described as a sort of water-clock. 
The water from the tap A flows into the funnel B, and falls from the 
nozzle of B into the glass tube C, hanging from one arm of the balance D. 
Despite the outflow from the tap E, C gradually fills up, and the balance 
beam tilts over. Owing to the presence of the weight F the action is 
sudden and definite, and in the course of the movement H comes in contact 
with N, the projecting arm of B, and pushes the latter, which is pivoted at 
