104 



MR. J. P. JOULE ON EXPERIMENTS ON THE 



The law is also verified so far as pressure is concerned 

 by the following tabulated experiments with tubes of 

 various lengths and diameters, but all terminated by a 

 short piece of wide pipe, three inches long by two and a 

 half inches in diameter, which was inserted into the 

 bellows : — 



Length & diameter 

 of tubes. 



Pressure. 



Cubic Inches of Air 



discharged per second 



per square inch 



aperture. 



Cubic inches of Air dis- 

 charged per second per 

 square inch aperture 

 divided by square root 

 of pressure. 



44 and 0-875 | 

 20 and 0-98 j 

 20 and I '594 \ 



I '44 

 3-52 

 1-44 

 3*52 

 1-44 



3-52 



562-9 

 909-7 

 671-5 



1049-4 

 710-6 



1117-1 



469-1 



484-7 



559'6 



559'i 

 592-2 



595'i 



At an early period of the research it was found that a 

 very slight bur or projection on the edge of the hole in a 

 thin plate produced a remarkable change in the quantity 

 of eiSuent air. I had holes of the respective least dia- 

 meters, o'S^S, o'7(55 ^^^ 1"^^ inch, cut out of a thin plate 

 of tinned iron by a brace-bit. A slight bur projected 

 to one-fortieth of an inch beyond the plain surface. The 

 following experiments were then made, using a pressure 

 of air equal to 1*44 inch of water : — 





Cubic inches of Air per second, reduced to one square inch of aperture. 1 



bur with respect 

 to the bellows. 



Hole of diameter Hole of diameter 

 0'535 inch. 0'75 inch. 



Hole of diameter 

 1-61 inch. 



Outwards 

 Inwards 



597*8 579'2 

 529'3 524*4 



647-4 

 584-7 



A hole one inch square, without any bur, gave ^6y cubic 

 inches per second. 



The influence of a tube in increasing the quantity of 

 effluent air has been already adverted to. It was a matter 

 of considerable interest to determine the length of tube 

 which would produce the maximum effect. In my first 

 experiments to determine this point, I employed a tube 



