1886.] Sir William Thomson on Caj>illary Attraction. 483 



WEEKLY EVENING MEETING, 



Friday, January 29, 1886. 



William Huggins, Esq. D.C.L. LL.D. F.E.S. Vice-President, in the 



Chair. 



Sir William Thomson, D.C.L. LL.D. F.E.S. M.B.I. 



Capillary Attraction. 



The heaviness of matter had been known for as many thousand years 

 as men and philosophers had lived on the earth, but none had 

 susiDOcted or imagined, before Newton's discovery of universal gravi- 

 tation, that heaviness is due to action at a distance between two 

 portions of matter. Electrical attractions and repulsions, and mac'- 

 netic attractions and repulsions, had been familiar to naturalists and 

 philosophers for two or three thousand years. Gilbert, by showing 

 that the earth, acting as a great magnet, is the efficient cause of the 

 compass needle's pointing to the north, had enlarged people's ideas 

 regarding the distances at which magnets can exert sensible action. 

 But neither he nor any one else had suggested that heaviness is the 

 resultant of mutual attractions between all parts of the heavy body 

 and all parts of the earth, and it had not entered the imagination of 

 man to conceive that different portions of matter at the earth's 

 surface, or even the more dignified masses called the heavenly 

 bodies, mutually attract one another. Newton did not himself give 

 any observational or experimental proof of the mutual attraction 

 between any two bodies, of which both are smaller than the moon. 

 The smallest case of gravitational action which w^as included in the 

 observational foundation of his theory, was that of the moon on the 

 waters of the ocean, by which the tides are produced; but his 

 inductive conclusion that the heaviness of a piece of matter at the 

 earth's surface, is the resultant of attractions from all parts of the 

 earth acting in inverse proportion to squares of distances, made it 

 highly probable that pieces of matter within a few feet or a few inches 

 apart attract one another according to the same law of distance and 

 Cavendish's splendid experiment verified this conclusion. But now 

 for our question of this evening. Does this attraction between any 

 particle of matter in one body and any particle of matter in another 

 continue to vary inversely as the square of the distance, when the 

 distance between the nearest points of the two bodies is diminished to 

 an inch (Cavendish's experiment does not demonstrate this, but makes 

 it very probable), or to a centimetre, or to the hundi-ed-thousandth 

 of a centimetre, or to the hundred-millionth of a centimetre ? 

 Now I dip my finger into this basin of water; you see proved 



