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MONDAY, MARCH 13th. 



BY 



C. H. DRAPER, B.A., D.Sc. (Lond.), 



Municipal School of Science and Technology. 



AS is the case with most of the deeper facts of physical science, 

 in dealing with the "skin of liquids" we are dealing 

 with something which is itself invisible. You cannot skin a 

 mass of water as you can a hare, and hold up the skin in omnium 

 conxpectu. But its existence may be proved by means of a 

 delicate little instrument devised by a physicist named Mens- 

 brugghe. Take a piece of cork, affix a ring of thin wire to one 

 end, and a weight to the other. Adjust the weight so that the 

 apparatus floats upright in water with the ring just above the 

 surface. Then take a small rod, and gently push the whole device 

 down under the water. Experience ought lead one to suppose 

 that on taking away the rod, the float would return to its first 

 position. If, however, the float be carefully balanced so that the 

 wire ring, on being alloAved to rise gradually, touches the surface 

 all round at the same time, the apparatus will rise no higher, — 

 showing that the film of water at the surface offers more resistance 

 to the passage of a solid body than either the water below or the 

 air above. 



A second experiment brings home the existence of the 

 " skin " in a more striking way. " Here we have a sieve with 

 very small meshes," said Dr. Draper, " and if water be poured 

 carefully into it, the water does not run through, because the 

 skin formed between the meshes blocks up the small holes. You 

 remember the people who, in the days of our childhood, when 

 nothing was impossible, went to sea in a sieve ? Well, I should 

 not mind going to sea now in a sieve, if I were allowed to make 

 the sieve, and have full command of the weather. Here is a 

 small sieve made of copper, which is nine times as heavy as 

 water, yet this sieve might be warranted to carry a small burden 

 on smooth water. It is, in fact, a boat floating with 10,000 

 holes in the bottom — the more holes the better for the boat." 



