230 WRITINGS OF JOSEPH HENRY. [1845 



tion. The difficulty consists in explaining how the attraction 

 of cohesion, Avhich becomes insensible at sensible distances, 

 should produce this effect. To explain this let us suppose 

 two substances uniformly diffused through each other by a 

 slight mutual attraction, as in the case of a lump of sugar 

 dissolved in a large quantity of water, every particle of the 

 water will attract to itself its proportion of sugar, and the 

 whole will be in a state of equilibrium. If the diffusion at 

 its commencement had been assisted by heat, and this cause 

 of the separation of the homogeneous particles no longer 

 existed, the diffusion might be one of unstable equilibrium; 

 and the slightest extraneous force, such as the attraction of 

 a minute piece of shell, might serve to disturb the quiescence, 

 and draw to itself the diffused particles which were immedi- 

 ately contiguous to it. This would leave a vacuum of the 

 atoms around the attracting mass, for example, as in the case 

 of the sugar, there would be a portion of the water around 

 the nucleus deprived of sugar; this portion of the water would 

 attract its portion of sugar from the layer without, and into 

 this layer the sugar from the layer next without would be 

 diffused, and so on until, through all the water, the remain- 

 ing sugar would be uniformly diffused. The process would 

 continue to be repeated, by the nucleus again attracting a 

 portion of the sugar from the water immediately around it, 

 and so on until a considerable accumulation would be formed 

 around the foreign substance. 



We can in this way conceive of the manner by which the 

 molecular action, which is insensible at perceptible distances, 

 may produce results which would appear to be the effect of 

 attraction acting at a distance. 



