282 Prof. W. 0. Unwin on the Discharge of Water 



It is not easy to see that any increase of fluidity of the water 

 or diminution of friction could do more than annul this loss of 

 from 3 to 6 per cent. Mr. Isherwood's experiments seem to 

 imply that the velocity of discharge at high temperatures may 

 be greater than the velocity due to the head. It seemed worth 

 while therefore to repeat the experiment. The means at the 

 author's disposal did not permit him to make the experiments 

 on quite so large a scale as those of Mr. Isherwood ; but it 

 was, he believes, quite large enough to indicate any gain of 

 velocity of the amount mentioned above. 



A cast-iron cistern was used, the interior bored out to a 

 diameter of 0*4 metre. The first orifice tried was a carefully 

 formed brass conoidal orifice, formed as nearly as might be to 

 the shape of the vena contracta, and very approximately 0*01 

 metre diameter. Three pointed indexes were fixed in the cis- 

 tern, below the surface of the water ; so that, as the level of 

 the water descended, the instant at which the point broke the 

 surface could be very exactly observed. Calling the levels of 

 the three indexes A, B, and C, the time was noted in which 

 the water-level descended from A to B and from A to C. A 

 chronograph-watch was used, the seconds' hand being started 

 at the moment the water-level was at A. When the level 

 reached B, the time elapsed was noted by an observer count- 

 ing seconds. When the level reached C the hand of the watch 

 was stopped. This last observation was perhaps more reliable 

 than the intermediate one at the level B. 



For the higher temperatures the water was taken from a 

 steam-engine boiler ; it was somewhat discoloured by iron 

 and sediment. The same water was used in the experiments 

 at lower temperatures, but in its ordinary clean condition. 

 The author does not think that the condition of the water made 

 any sensible difference in the results of the experiments. 



Experiments on a Conoidal Orifice^ June 4, 1878. 

 Time of fall of water-level 

 Temperature, in seconds. 



Fahrenheit. ,. A x 



From A to B. From A to C. 



190 59 89 



190 58J 8S± 



130 59£ 90 



60 62 93 



60 61J 92i 



Mean Results. 



190 58-75 88-75 



130 59-5 90-00 



60 61-75 92-50 



