ESSAYS 



THE ELECTRICAL BASIS OF COHESION (Herbert Chatley, 

 D.Sc. Lond., Research Engineer to the Whangpoo Conservancy Board, 

 Shanghai). 



It cannot but have been observed that there is a considerable hiatus in scientific 

 knowledge of the properties of matter between the behaviour of the atom and the 

 mechanics of visible masses. While microscopic investigation of crystalline 

 structure and of the Brownian movement in liquids has somewhat narrowed this 

 field of ignorance, it is not too much to say that the actual nature of molecular 

 force as distinct from the atomic force which produces chemical change remains 

 to a great extent a mystery, particularly in the case of the solid state, where its 

 influence is preponderant. 



Engineers have acquired an immense amount of information as to the " strength 

 of materials," and based thereon is an elaborate mathematical structure termed 

 the " theory of elasticity," but the relation of the cohesive forces, which manifest 

 as " strength " and " elasticity," to electrostatic, magnetic, or gravitational forces 

 is unsolved. 



Kelvin {Popular Lectures, vol. i., and Proc. Roy. Soc. Edin., April 21, 1862) 

 opined that very great density of the molecules would explain cohesive attraction 

 in accordance with the Newtonian law for gravitation, but it is not difficult to 

 show that this hypothesis is incorrect. Recent work shows that the mass of an 

 iron molecule Fe 3 is about i"86 x io -82 grams, and the distance from centre to 

 centre of a pair of molecules in a solid is about 3'o x io _8 cm. Applying the 

 Newtonian rule to these quantities we find that the gravitational bond is about 

 2'5 x 10 _36 dynes. Quantities of a similar order are obtained with other 

 molecular pairs, since the molecular interval increases with (but not so fast as) the 

 molecular weight. 



It is of course irrelevant to point out that even if this hypothesis were true no 

 further light would be shed on the nature of gravitation itself, but there would 

 only remain one generality to compare it with, viz. electrostatic force. If 

 Sutherland's hypothesis as to the force of gravitation being a differential effect 

 of positive and negative tractations and pellations is accepted, nothing further 

 would be required to give a complete theory of tractation on an electrical 

 basis. 



Nernst and his collaborators, on the basis of crystal architecture, consider that 

 cohesion is identical with chemical affinity. Against this it must of course be 

 objected that cohesion appears to be always active at minute distances even for 

 neutral molecules, is not necessarily vectorised, and seems to be weaker than the 

 feeblest chemical linkage. 



The tractation between two dissimilar unit charges at a distance of 3'o x 10 ~ 8 

 cm. is 2*5 x io -4 dynes. 



(It should here be remarked that the absolute ratio of electrostatic tractation 

 to gravitational tractation for equal masses at equal distances is io 43 .) 



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