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THE POPULAR SCIENCE MONTHLY. 



planation that next suggests itself depends on the acceleration of 

 velocity during the fall, which should have as a necessary result 

 a progressive diminution of the section-surface. It may be proved 



experimentally that this has nothing 

 to do with the triangular form by 

 giving an upward direction to the 

 jet from a flattened tube ; the stream 

 takes the form of a tongue all the 

 same (Fig. 10). 



Is it because the lateral parts of 

 the liquid ribbon, having to overcome 

 in the canal or the tube a more con- 

 siderable friction than in the central 

 part of the current, have at their issue 

 a less mean velocity than the latter,, 

 and are therefore attracted by them ? 

 The effect incontestably exists ; but 

 we shall demonstrate, when we come 

 to speak of the liquid vein, that it 

 is negligible in comparison with an- 

 other cause. After trying these va- 

 rious causes and eliminating them 

 one after the other, we are brought 

 to the conclusion that the essential 

 cause that draws toward the middle 

 the edges of a liquid sheet falling 

 freely is the force of cohesion, or 

 capillary tension. It is the same force that causes a freely sus- 

 pended liquid mass to take the spherical form, as in Plateau's, 

 well-known experiment, and in the world of the stars. It is only 

 in this state of least surface that the attractions between the mole- 



Fig. 8. Form and Constitution of 

 a Liquid Sheet falling. 



Fig. 9. 



Fig. 10. Tongue- like Form of a Jet of Water 

 spurting from a Flattened Tube. 



cules are in equilibrium. A falling liquid sheet will, therefore,, 

 tend toward a cylindrical or contracting form. Does it really be- 

 come a cylinder and keep the form ? What takes place lower 

 down ? These questions require knowledge of other peculiarities 

 of the primary tongue. 



When water is subjected to a shock or to pressure, the pressure 

 does not distribute itself insensibly through all the mass with 



