356 SCIENTIFIC THOUGHT. 



atmosphere, into or in the neighbourhood of solid bodies. 

 He conceived light to be a material substance, consisting 

 of minute particles, propelled in straight lines from the 

 luminous centres. These small particles, when arriving 

 at or near the surface of transparent bodies, came under 

 the influence of an attraction from the substance of such 

 bodies, and Newton succeeded in showing that for rays 

 of light which fall on transparent surfaces at an angle, 

 the path of the ray in the body would be deflected accord- 

 ing to the rule experimentally determined by Snell, and 

 published by Descartes. This application of the idea of 

 attraction, or action at a distance, to very small or mole- 

 cular dimensions, required a modification of the gravita- 

 tion formula. The first who took an important step farther 

 in this direction was Francis Hauksbee. Between the 

 years 1709 and 1713 he made a series of experiments on 

 32. what is called capillary action. His experiments were 



Capillary 



action. discussed by Newton in the later editions of the ' Opticks/ 

 and followed by those of Dr Jurin in 1718. Hauksbee, 

 Newton, Jurin, and subsequent writers, like Clairaut, all 

 attributed these and similar phenomena to molecular 

 attractions, and Laplace showed that for the mathematical 

 treatment of the subject a knowledge of the exact law 

 (corresponding to the Newtonian law of molar attraction) 

 was unnecessary, but that it was necessary and sufficient to 

 assume the existence of an attraction of the molecules of 

 bodies, which decreases very rapidly as their distances in- 

 crease, "so as to become insensible at the smallest distances 

 perceptible by our senses." l The phenomena of atmos- 



1 See ' Me"canique celeste,' vol. 

 iv. (1805), Supplement, p. 67. See 

 also p. 2 : " J'ai cherche", il y a long- 



temps, a determiner les lois d'at- 

 traction qui repre"sentent ces phe"- 

 nomenes : de nouvelles recherche& 



