190 Prof. Magnus's Hydraulic Researches. 



90. If a solid body which has a greater specific gravity than 

 water be laid on the surface of water, the latter is pressed aside, 

 but unites again immediately over the body. But if the body falls 

 from some height into the water, the latter receives at the place 

 where it is first met a strong push, which moves it further on 

 one side than would be necessary to make room for the pushing 

 body. This process is repeated in the strata immediately below 

 the surface, and in this way a cavity is formed in the water which 

 has a greater section than the falling body. But siuce the mo- 

 mentum of the latter in its further motion is lessened by the 

 resistance which it experiences, at a greater depth it moves the 

 water less ou one side. Hence the cavity at a greater depth is 

 narrower, until at length the momentum whicli the body has 

 received by its free fall on the surface is destroyed, and its 

 further sinking occurs just as if it had been tranquilly laid on 

 the water, which is now only so much moved aside as its mag- 

 nitude necessitates. 



91. If the falling body, on meeting the water, possesses any 

 considerable moving force, the cavity extends so far down that 

 the water meets ou the surface and closes before its formation 

 below is completed. Hence air is enclosed, which afterwards 

 reaches the surface in the form of a bubble. 



92. It is scarcely necessary to mention, that bubbles are 

 formed in exactly the same way if, instead of a solid body, single 

 drops of water fall into the water. 



The cup-shaped cavity which drops of water produce can be 

 distinctly observed by letting them fall into water which is con- 

 tained in a glass vessel, and looking at the superior stratum of 

 liquid from the side through the water. 



93. It might be believed, that a cavity whose section is greater 

 than that of the falling diop or solid body, was not necessary for 

 the production of air-bubbles ; for if the water did not separate 

 further than the section of the body requires, air would also be 

 enclosed, if this body only moved quickly enough so that it 

 might have reached a sufficient depth below the surface before 

 the water above had joined. It is easy to show, that, if this were 

 the case, the quantity of air would be far too small to produce 

 the bubbles which are actually observed. For if small solid 

 bodies, for instance shot, be let fall into a vessel which contains 

 a stratum of water 2 centims. high, then if the shot fall from a 

 height of l'^"25, air-bubbles are obtained whose contents are 

 many times greater than those of a cylinder of the height of 

 the water and the diameter of the falling shot. This phseno- 

 menon is more surprising when peas, instead of shot, are used. 

 It is only necessary to think of the great bubbles which are 

 fcrmed by rain-drops falling almost vertically into shallow masses 



