252 Mr. William Sutherland on the 



intensity less as the liquid is more viscous and as the granules 

 are larger. It occurs when every precaution is taken to en- 

 sure constant temperature, and to ensure the absence of all 

 external causes of motion. Granules of the same size but as 

 different in character as solid granules, liquid globules, and 

 gaseous bubbles, show but little difference in their motions — a 

 fact which proves that the cause is to be looked for not in the 

 granules themselves but in the liquid, the granules being 

 merely an index of motions existing in the liquid. The most 

 pronounced character of the motion is its rapid increase with 

 diminishing size of granules, so that all that is seen under the 

 microscope is the limit of movements of unknown magnitude. 

 Gouy considers the Brownian movements to be a remote 

 result of the motion of the molecules themselves, but according 

 to what we know of molecular dimensions I fancy that the 

 Brownian movement must be considered rather as a sign of 

 the motion of swarms of molecules. If swarms of molecules 

 are weaving in and out amongst one another, so that the 

 average transfer of momentum at a point is the same in all 

 directions, then the vibratory agitation of granules amongst 

 the swarms is just what we should expect. The striking fact 

 about the Brownian movement is that it is ceaseless ; it is 

 never degraded into heat. This alone forces us to conceive a 

 form of motion existing in liquids on a larger scale than 

 molecular motion but possessing its character of permanence ; 

 in other words, the motion of swarms of molecules. 



The existence of swarms would not affect our views of the 

 rise of liquids in capillary tubes as a purely statical question; 

 so that, for the connexion between molecular force and 

 surface-tension, we can use the calculation given in another 

 paper (Phil. Mag. April 1889) (rather badly affected with 

 misprints), where I have shown that the surface-tension of 

 liquids that wet glass, measured in tubes so narrow that the 

 meniscus-surface is a hemisphere, is given by the equation 



*=7rp 2 Ae/{2+s/2); 

 where p is the average density of the capillary surface-film 

 (to be written also 1/v), and e is the distance which we must 

 suppose to be left between a continuous meniscus and the base 

 of a continuous column raised by its attraction, if the action 

 between the continuous distributions is to be the same as in 

 the natural case of discontinuous molecular constitution of 

 meniscus and column. The distance e is not identical with 

 the length a which occurs in our theoretical value of the 

 internal virial of unit mass, 



A^(31og2L/a-4) = |i, 



