PASSAGE OP AIR THROUGH PIPES AND APERTURES. 107 



back to the air rushing through the orifice if its velocity 

 be not greater than 1090 feet per second. I have failed, 

 however, to discover any sensible influence from this cause 

 on the velocity of efflux. It occurred to me also to try 

 whether the air issued with a rotary motion ; but such 

 experiments as I have been able to make with vanes have 

 led me to no decisive conclusion, although there can be 

 no doubt that many circumstances might cause such vor- 

 tices, the operation of which would be to diminish the 

 velocity of efflux. 



