NEW CONCEPTIONS IN SCIENCE 



thirtieth of a micro-micron. This fixed a lower 

 limit. 



Then there was the familiar attraction between 

 water and glass, illustrated in the e very-day fact 

 that we can fill a glass higher than the brim, or 

 that when a tube of very small diameter is dipped 

 in water the water will rise several inches in the 

 tube, in apparent violation of the law of gravity. 

 This is capillary (hairlifti) attraction. Close of 

 kin is the force (the so-called surface tension) 

 which makes water and all other liquids form in 

 drops. This is what holds a soap-bubble together. 

 It is possible to measure this force very definitely, 

 slight as it is, and from this to calculate the dis- 

 tance at which its effect would be inappreciable. 

 This is reckoned at 0.2 /uji. By a quite indepen- 

 dent method Lord Kelvin reached the conclusion 

 that there could not be several molecules in half 

 this thickness a most striking agreement. It was 

 exactly as if two geometers, employing entirely 

 different means, should compute the distance from, 

 say, Cape Nome in Alaska to Cape Horn in far 

 Patagonia, and that their estimates should agree 

 within a fraction of a mile. 



By far the most accurate method, however, lies 

 in the behavior of gases, like the air. When, for 

 example, some ill-smelling gas is set free in a room, 

 it takes a definite time for the smell to penetrate to 



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