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XXXV III. On the Discharge of Water from Orifices at diffe- 

 rent Temperatures. By Professor W. C. Unwin, M.I. C.JE* 



IN the Journal of the Franklin Institute for May 1878, 

 there is a paper by Chief-Engineer Isherwood, of the 

 U.S. Navy, giving an account of some experiments on the 

 discharge of water from orifices at different temperatures. 

 Those experiments appear to have been made on a sufficient 

 scale and with very great care ; and they lead to the conclusion 

 that temperature has a very marked influence on the discharge. 

 The author evidently supposes his conclusions to be applicable 

 to orifices in general ; for he remarks that, " in the various de- 

 terminations which have been made of the ratio of the actual 

 to the theoretical discharge of water through orifices, the tem- 

 perature of the water should have been noted. The experi- 

 mental ratios are true for only the experimental temperatures, 

 and need reduction to a standard temperature." 



The experiments were made by noting the time in which 

 the level of the water in a cylindrical vessel fell from one level 

 to another, the water being discharged from a given orifice. 

 The observed results of the experiments are not given. These 

 results were plotted in a diagram, and a fair curve drawn pass- 

 ing as evenly as possible through the plotted points. The 

 results are stated to have been corrected for the dilatation of 

 the orifice by heat ; but it is not stated whether any correction 

 was made for the dilatation of the volume of the vessel from 

 which the water flowed, a correction quite as important as the 

 other. The following short Table gives a few of Mr. Isher- 

 wood's results, as measured by him from the curve represent- 

 ing the observed results : — 



Temperature, .Relative time Relative velocities 



Fahrenheit. of discharge for of discharge for 



equal volumes. equal volumes. 



32 1-0000 1-0000 



60 0-9896 1-0105 



100 0-9696 1-0313 



140 0-9457 1-0577 



180 0-9156 1-0922 



212 0-8855 1-1293 



Thus the velocity of discharge increases 12 per cent, as the 

 temperature rises from 32° to 212°, and it increases 8 per 

 cent, as the temperature rises from 60° to 180°. 



Now there is this difficulty in accepting the results of Mr. 



Isherwood's experiments, — that the actual velocity of discharge 



at ordinary temperatures differs from the whole velocity due 



to the head by only from 3 to 6 per cent, for simple orifices. 



* Communicated bv the Physical Society. 



