102 MR. J. P. JOULE ON EXPERIMENTS ON THE 



IV, — Eoeperiments on the Passage of Air through Pipes, 



and Apertures in thin plates. 



By J. P. Joule, LL.D., F.R.S., ^c. 



Eead April 3rd, 



Sir Isaac Newton, Polenus, Daniel Bernoulli and others 

 have observed that water, when it is made to flow out of a 

 vessel through a hole cut in a thin plate, becomes con- 

 tracted in diameter and increased in velocity at a short 

 distance from the hole, the ratio of the diameter of the 

 stream at its narrowest part to the diameter of the hole 

 being, according to Newton's experiments, as twenty-one 

 to twenty-five. The phenomenon is occasioned by a con- 

 course of the particles of water as they enter the orifice, 

 and may, as Venturi has shown, be obviated by employing 

 a short pipe instead of a hole in a thin plate. 



Air, and other fluids are known to comport themselves 

 in the same manner as water. The subject is one of con- 

 siderable importance, and as I have had an opportunity of 

 trying some experiments on it, I trust they will be found 

 of sufiicient interest to warrant my ofiering them to the 

 notice of the Society. 



The principal part of my apparatus was a large organ- 

 bellows, which, by means of weights laid on the top could 

 be worked at pressures varying from 1*44 to g'G^ inches 

 of water as indicated by the difierence of level of water 

 in a bent glass tube. A circular hole, two and a half 



