486 Sir William Thomson [Jan. 29, 



the distance becomes less than 50 micro-millimetres is proved to be 

 insufficient, may we not go farther and say that it is unnecessary to 

 assume any deviation from the Newtonian law of force varying 

 inversely as the square of the distance continuously from the 

 millionth of a micro-millimetre to the distance of the remotest star or 

 remotest piece of matter in the universe ; and, until we see how 

 gravity itself is to be explained, as Newton and Faraday thought it 

 must be explained, by some continuous action of intervening or sur- 

 rounding matter, may we not be temporarily satisfied to explain 

 capillary attraction merely as Newtonian attraction intensified in 

 virtue of intensely dense molecules movable among one another, 

 of which the aggregate constitutes a mass of liquid or solid. 



But now for the present, and for the rest of this evening, let us 

 dismiss all idea of molecular theory, and think of the molar theory 

 pure and simple, of Laplace and Gauss. Eeturning to our two pieces 

 of rigidified water left at a distance of 250 micro-millimetres from 

 one another. Holding them in my two hands, I let them come 

 nearer and nearer until they touch all along the surfaces A and B. 

 They begin to attract one another with a force which may be scarcely 

 sensible to my hands when their distance apart is 50 micro- 

 millimetres, or even as little as 10 micro-millimetres ; but which 

 certainly becomes sensible when the distance becomes one micro- 

 millimetre, or the fraction of a micro-millimetre ; and enormous, 

 hundreds or thousands of kilogrammes' weight, before they come 

 into absolute contact. I am supposing the area of each of the 

 opposed surfaces to be a few square centimetres. To fix the ideas, 

 I shall suppose it to be exactly thirty square centimetres. If my 

 sense of force were sufficiently metrical I should find that the work 

 done by the attraction of the rigidified pieces of water in pulling my 

 two hands together was just about 4^ centimetre-grammes. The 

 force to do this work, if it had been uniform throughout the space of 

 50 micro-millimetres (five-millionths of a centimetre) must have been 

 900,000 grammes weight, that is to say, nine-tenths of a ton. But 

 in reality it is done by a force increasing from something very small 

 at the distance of 50 micro-millimetres to some unknown greatest 

 amount. It may reach a maximum before absolute contact, and then 

 begin to diminish, or it may increase and increase up to contact, we 

 cannot tell which. Whatever may be the law of variation of the 

 force, it is certain that throughout a small part of the distance it is 

 considerably more than one ton. It is possible that it is enormously 

 more than one ton, to make up the ascertained amount of work of 4J 

 centimetre-grammes performed in a si^ace of 50 micro-millimetres. 



But now let us vary the circumstances a little. I take the two 

 pieces of rigidified water, and bring them to touch at a pair of 

 corresponding points in the borders of the two surfaces A and B, 

 keeping the rest of the surfaces wide asunder (see Fig. 1). The 

 work done on my hands in this proceeding is infinitesimal. Now, 

 without at i>ll altering the law of attractive force, lot a minute film 



