33 Prof. Magnus on the Motion of Fluids. 



of the watev-bellowsj I have constructed a model with glass in 

 the manner represented by fig. 14. 



N is the water -holder, in which, by means of a cork, the tube 

 ab, 6 inches long, is fastened. The lower end of ab dips above 

 into the tube cd. The latter is 6-5 feet long, and has an inner 

 diameter of fths of an inch ; at rf it pierces a cork, which closes 

 the bottle AB, and it ends at (/ about 3 inches above the bottom of 

 the bottle. Through the cork d two other tubes are introduced ; 

 de, which can be closed by means of the cock e, and hik, which 

 serves as a manometer, and is tilled with mercury to k. 



When the tube ab had an opening at its lower end 0*4 of an 

 inch in diameter, as the water flowed through it downwards, a 

 considerable portion of air was carried along with it into the 

 bottle AB. The pressure increased, and as the mercury ascended 

 in k the water ascended in the tube cdff. By means of the cocks 

 e and D, the escape of the air and water was so regulated that 

 the water-height in cdg remained constant. When this height 

 was about 3 feet over the surface of the water in the bottle, the 

 opening, as already stated, being 0'4 of an inch wide, a midtitude 

 of small bubbles were seen to descend with the water through 

 the entire breadth of the tube. When the diameter was greater, 

 the motion was quicker, so that the course of the bubbles could 

 not be exactly followed. When, on the contrary, the opening b 

 was smaller, for example 0*3 of an inch in diameter, air-bubbles 

 were observed at/, but they could not penetrate to the lower 

 end of the tube ; as soon as they had attained a certain depth, 

 they rose again in consequence of their small specific weight. 

 Small isolated bubbles only were able to penetrate to a depth of 



34 inches. 



It is endent that the bubbles are formed at the point where 

 the falling water meets the surface /"; here they are quite en- 

 closed by the water, and carried with it downwards. If the 

 force which causes this motion be so great that the bubbles de- 

 scend more quickly than they would arise in consequence of 

 their small specific gravity, then they will reach the bottle AB. 

 This, however, can only take place when the water falls from a 

 sufficient height, and when the opening h bears a sensible ratio 

 to the diameter of the tube cdff. If the opening b bear only a 

 small ratio to the tube cdff, the motion of the water in the latter 

 is feeble, and consequently the bubbles move more quickly up- 

 wards than downwards. 



If the opening be not much smaller than the tube cdff, the 

 falling water closes tip the latter, even when the tube, instead of 

 reaching to ff, ends immediately under the cork d. The water 

 then stands at a height within the tube corresponding to the 

 air-pressure in the bottle underneath, and in general exactly the 

 same effects are observed as when the tube cd penetrates the sur- 



