Motion of Gases. 383 



counted from the moment the finger is removed till the water 

 flics out at a. Hence, knowing the capacity of the vessel and 

 the area of the aperture, we obtain the velocity. If the tube TB 

 should be continued nearly to the bottom of A, while A was filling 

 with water, the length of the compressing column would be 

 gradually diminished, and consequently the pressure constantly 

 changing. To avoid any irregularity from this cause the open 

 end of the tube is placed as near the top of the cask as is 

 consistent with a free passage for the water. 



The vessel was made to contain 1 5 lb< 6 OZ< of water, from which 

 its capacity is found to be 425,088 cubic inches. The area of 

 the aperture f a through which the water is discharged was 0,0046 

 inches. 



(1.) The altitude of T above the cask being 30 inches, the 

 time of expelling the air was found by several trials to be 33". 



(2.) The altitude of T being 6 feet, the time of expelling the 

 air was 21,3". 



In the first experiment, 425,088, the capacity of the cask, being 

 divided by 0,0046, the area of the aperture, gives 92410,4 inches 

 for the length of the stream continued during 33". Hence 



g 2410 ' 4 = 233,3 feet, the velocity per second. 

 12X33 



From the second experiment we deduce by a similar process, 

 361,6 for the velocity per second; and to show the correspond- 

 ence of this with the- first, we use the proportion 



: : 233,3 : 361,8, 

 differing from the experimental result one fifth of a foot. 



496. To compare the velocity thus found by experiment with 

 that assigned by theory, we use the proportion 



\/6 : V34 : : 361,6 : 860,5, 



the velocity with which the atmosphere would begin to enter a 

 void. Taking the result before found, namely, 1338, and multi- 

 plying it by 0,63, agreeably to what is laid down in article 479, 



