Prof. Magnus on the Motion of Fluids. 7 



fg, the velocity with which the water passes through it be de- 

 creased. It follows from this, that the pressure at m depends 

 as well upon the velocity of the jet as upon the ratio of the dia- 

 meters of the two tubes ^ and f/e*. 



When the orifice / of the narrow tube does not reach to the 

 point at which the perpendicular tube mn is attached, but is so 

 far distant from this point that the water when it passes m has 

 already moved through a portion of the tube de without altera- 

 tion of its diameter, and consequently without change of velocity, 

 then the water rises in the tube mn, and stands therein higher 

 than in the vessel A. 



15. As long as the eifervescence continues in the tube de, air- 

 bubbles are observed to enter the vessel A also ; for as the 

 whole of the water contained in the tube passes into this vessel, 

 the air inclosed in the foam will be carried in along with it. 

 The extent to which this takes place can be readily observed 

 when the tube de, tig. 9, is of glass, and of tolerable length, say 

 2 feet long. The fluid is then seen to eflPervesce in the forward 

 portion at k; thence, however, it flows or is moved towards d, 

 the small air-bubbles upon its upper siuiace being carried for- 

 ward along with it. This takes place even when the tube de is 

 so inclined that the foam might be expected to move in a con- 

 trary direction ; that is to say, when the end d, by which the 

 tube is fastened in the vessel A, is lower than the end e. 



The entering of such air-bubbles with the water has been 

 already observed by Savart, who, however, has paid no further 

 attention to the matter. I am, notwithstanding, of opinion that it 

 is not altogether unimportant . Who has not observed the bubbles 

 which exhibit themselves when water is poured into a glass ? and 

 yet this effect, which has been observed from the earliest times, 

 remains as yet without explanation, or at least the explanations 

 which have been attempted are by no means sufficient. 



16. Ventm-i, as already mentioned in § 2, is of opinion that 

 the water -jet carries the air along with it. According to this 

 view, the entering of the air into the fluid is attributed to 

 the friction between the air and the jet. But if the phse- 

 nomenon be regarded with some attention, it will be impos- 

 sible to accept this explanation; for it is incredible that the air 

 should cling to the jet with a force sufticieut to carry it deep 

 under the surface of the water. 



17. In order completely to refute this notion, I permitted a 



* Exactly similar effects are obtained when two tubes, a narrow and a 

 wide one, are connected together ; if a third tube issuing from the place 

 where both are united, he allowed to dij) into a vessel of mercury or of 

 water, the fluid will ascend in this tube when a current of air is blown from 

 the narrow to the wide one. 



