August 31, 1906.] 



SCIENCE. 



26: 



1. The coefficient of discharge by direct 

 measurement in a calibrated hydraulic cis- 

 tern, (a) to verify existing constants, and 

 (&) to find the coefficient of velocity for 

 comparison with that given by the Pitot 

 tube, and (c) to verify its constant. The 

 results show a decrease in the coefficient of 

 discharge of 2.5 per cent, with an increase 

 in the diameter of the orifice from three 

 fourths inch to two and one half inches. 

 The average value obtained was 0.60664, 

 and is about 1.8 per cent greater than 

 that givea in Merriman's 'Hydraulics' 

 (0.5960). Compared with that of Bovey 

 (0.6000), the result obtained with the jet 

 from the one inch orifice (0.6097) is 1.6 

 per cent, higher. 



2. The shape of the jet in the vicinity of 

 the least section as found by exploring the 

 contour of the jet by the special micrometer 

 caliper. It was found that the distance 

 from the face of the orifice to the least 

 section of the jet varied from 1.6 radii for 

 the three fourths inch orifice 'to about one 

 radius for that two and one half inches in 

 diameter. Text-books on hydraulics give 

 this distance as being one radius, while 

 Bazin found no 'minimum section' of the 

 jet flowing through a large orifice and 

 under low head. 



3. The diameter at least section, as found 

 by the special caliper for four different 

 positions, 45° apart From the average 

 diameters, the coefficients of contraction 

 were computed, and they were found to 

 decrease from 0.6134 for the three fourths 

 inch orifice to 0.5955 for the two and one 

 half inch orifice, with an average value of 

 0.60674, As calculated from the average 

 results for the coefficients of discharge, the 

 coefficient of velocity is the quotient of the 

 coefficients of discharge and contraction, or 

 0.60664 divided by 0.60674 equals 0.99983. 

 From this result it is thought that the term 

 ' f rictionless orifice' is justifiable. 



4. The effect of increase of static pres- 



sure on least section. No appreciable in- 

 crease was found in the diameter of the least 

 section of the jet from a one inch orifice 

 by increasing the pressure from 5 pounds 

 to 100 pounds; and, for pressures as high 

 as 40 pounds, only a slight increase was 

 noticed for the orifices one and one half 

 inches to two and one half inches in diam- 

 eter. This latter was probably due in part 

 to the increased roughness of the contour 

 of the larger streams. 



5. The velocity in the least section was 

 found by traversing the jet with a one 

 fourths inch Pitot tube used in connection 

 with a differential manometer. It is 

 thought that the coefficient of velocity as 

 determined by the Pitot tube is unity 

 within a negligible fraction of 1 per cent, 

 and that the velocity is uniform through- 

 out the section. As calculated from the 

 average values of the coefficients of dis- 

 charge and contraction as determined by 

 experiment, the coefficient of velocity was 

 found to be 0.99983. This compares very 

 well with the average value of the coeffi- 

 cient of velocity, 0.99993, determined by 

 means of the Pitot tube. This would seem 

 to verify the statement that the Pitot con- 

 stant is unity. 



The paper shows that it is the result of 

 most careful and elaborate investigations. 

 It also shows the inaccuracy of certain 

 statements which are still being published 

 in books on hydraulics concerning the vena 

 contracta. While adding new facts to our 

 knowledge, it gives us a method for meas- 

 uring quantities of water discharged, and 

 with a probable error which is known to be 

 small and less than the probable error of 

 observation. The paper is worthy of care- 

 ful study and attention. It will probably 

 be published in the Engineering News. 



The next paper on the program was on 

 'Some Aspects of the Panama Canal,' by 

 Wm. H. Burr, professor of civil engineer- 

 ing, Columbia University, New York, N. 



