296 THE SCIENTIFIC PAPERS OF 



In answer to remarks by various speakers, 



MR. SIEMENS replied that the tendency of the drum to overrun, 

 when the discharge was stopped, was now successfully prevented 

 by the retarding vanes fixed upon it, by the resistance of which in 

 the stationary water it was speedily brought to rest. It had been 

 ascertained by experiment, that when the drum was rotating at 

 2000 revolutions per minute, only 5 or 6 revolutions were made 

 by it after the discharge had been suddenly stopped ; and the 

 little error arising from this cause was nearly compensated for by 

 the effect produced by the inertia of the drum at the commence- 

 ment of motion, a small quantity of water having to pass through 

 the drum not registered, before the drum had attained the velocity 

 corresponding with the velocity of the water through the meter. 

 As an extreme test, he might mention an instance in which a 

 meter had been used to measure the water supplied to an engine 

 boiler, and had been placed between the feed pump and the boiler, 

 and consequently the drum was set in motion and stopped at each 

 stroke of the pump, and went with jerks ; but even under this 

 severe trial the meter was found to register only about 5 per cent. 

 in excess. In such a case it would be necessary to provide an air 

 vessel to equalize the flow through the meter ; but even without 

 such an addition the amount of loss at each stoppage was evidently 

 very small. 



For lubrication common oil was not suitable, but any oil might 

 be used that was not acid, so as not to act upon the brasswork ; 

 pure olive oil and neat's foot oil answered well, or the oil extracted 

 from peat. As a further precaution against corrosion the brass- 

 work was tinned, and the success of the result was shown in the 

 meter exhibited by Mr. Bell, which he had not seen before, and in 

 which there was scarcely any wear after two years' work. This 

 result might appear remarkable, considering the high velocity of 

 the drum, but he thought that the higher the velocity the less 

 wear there would be upon the bearings, because the drum would 

 spin round in the manner of a top or gyroscope and require in 

 that state no lateral support whatever. 



