]06 MR. J. P. JOULE ON EXPERIMENTS ON THE 



My last experiment was with a hollow cone, the sides of 

 which formed an angle of 60°, and the opening at one end 

 was three inches, and at the other o'Sz^ in diameter. 

 Using a pressure of i"44, the quantities of effluent air per 

 second per square inch of narrowest aperture were, ac- 

 cordingly as the air entered at the broad or narrow aper- 

 tures, 666 "i and 51 0*7 respectively. 



The height of a column of air of the density and tem- 

 perature of that used in the experiments, which would 

 give a pressure of i'44 inches of water, is 88*93 feet. The 

 formula for very small pressures is v = \/2^h. Thus the 

 theoretical velocity in the absence of disturbing causes 

 would be 7<5"64 feet per second, which gives goyy cubic 

 inches issuing per second through an orifice one inch 

 square. Calling this theoretical efflux unity, the above 

 experiments give — 



For apertures in thin plates ----- "6074 

 For a tube of the same diameter as length - 'yGyG 

 For a similar tube with a v/ide entrance tube '8933 



I have not been able to detect any effect due to vibra- 

 tion of the issuing stream. By placing the end of a tube 

 composed of thin metal, four feet long and one inch dia- 

 meter, at about half an inch distance from an aperture in 

 a thin plate of one inch diameter, musical tones were 

 produced, which by increasing the pressure gradually, 

 ascended in harmonics through a scale of many octaves. 

 The same musical effects could be produced, using a con- 

 stant pressure of air, b}^ moving the tube nearer the aper- 

 ture through the space of a tenth of an inch. Savart and 

 Masson have adduced facts of this kind to prove that air 

 rushing out of an aperture has a vibratory motion. Al- 

 though I do not admit this conclusion, there can be no 

 doubt that the vibration constituting sound, produced by 

 such methods as above indicated, will be able to travel 



