in Fluids i 361 



and, consequently, would come into contact with at least 

 six hundred thousand different particles of water in that 

 time. 



Hence it appears how inconceivably short the time 

 must be that an individual particle, in motion, of any 

 Fluid, can remain in contact with any other individual 

 particle, not in motion, against which it strikes in its 

 progress, however slow that progress may appear to us to 

 be through the quiescent mass of the Fluid ! 



Supposing the contact to last as long as the moving 

 particle employs in passing through a space equal to the 

 length of its diameter, — which is evidently all that is 

 possible, and more than is probable ; then, in the case 

 just stated, the contact could not possibly last longer 

 than -f-Q 0^o"o" P^''^ ^^ ^ second ! This is the time which 

 a cannon bullet, flying with its greatest velocity (that 

 of 1600 feet in a second) would employ in advancing 2 

 inches. 



If the cannon bullet be a nine ■pounder^ Its diameter 

 will be four inches ; and if it move with a velocity of 

 1600 feet (= 19200 inches) in a second, it will pass 

 through a space just equal to 4800 times the length of 

 its diameter In i second. But we have seen that a par- 

 ticle of water moving -^\-^ of an inch In a second actually 

 passes through a space equal to loooo times the length 

 of its diameter in that time. Hence it appears that the 

 velocity with which the moving body quits the spaces it occu- 

 pies is more than twice as great in the particle of water 

 as in the cannon bullet ! 



There is one more computation which may be of use 

 in enabling us to form more just Ideas of the subject 

 under consideration ; and surely too much cannot be 

 done to enlighten the mind, and assist the imagination. 



