ON DOSCOVICH'S THEORY.* 



By Sir William Thompson. 



Without accepting Boscovicli's fuudaiiieutal doctiine tiiat the ulti- 

 mate atoms of matter are points endowed each with inertia and witli 

 mutual attractions or repulsions dependent on mutual distances, and 

 that all the properties of matter are due to equilibrium of these forces, 

 and to motions, or changes of motion produced by them when they are 

 not balanced, we can learn sometljing towards an understanding of the 

 real molecular structure of matter, and of some of its tliermo-dyuamic 

 properties, by consideration of tht; static and kinetic i)roblems which 

 it suggests. Hooke's exhibition of the forms of crystals by piles of 

 globes, jSTaviers' and Poisson's theory of the elasticity of solids. Max- 

 well's and Chiusius' work in the kinetic theory of gases, and Tait's 

 more recent work on the same subject — all developments of Boscovich's 

 theory pure and simple — amply justify this statement. 



Boscovich made it an essential in his theory that at the smallest dis- 

 tances there is repulsion, and at greater distances attraction; ending 

 with infinite repulsion at infinitely small distance, and with attraction 

 according to Newtonian law for all distances for which this law has 

 been proved. He suggested numerous transitions from attraction to 

 repulsion, which he illustrated graphically by a curve — the celebrated 

 Boscovich curve — to explain cohesion, mutual pressure between bodies 

 in contact, chemical aflSnity, and all possible properties of matter — ex- 

 cept heat, which he regarded as a sulphureous essence or virtue. It 

 seems now wonderful that after so clearly stating his fundamental pos- 

 tulate which included inertia, he did not see inter-molecular motion as 

 a necessary consequence of it, and so discover the kinetic theory of heat 

 for solids, liquids, and gases; and that he only used his inertia of the 

 atoms to explain the known phenomena of the inertia of palpable masses, 

 or assemblages of very large numbers of atoms. 



*A coniinimication to Section A of t 1r; Jiritisli Association A. >S., at Newcastle, Sep- 

 tember 13, 1839. (Report of Ike nritiah .Ismeiatioti, vol. Lix, pp. 4'Jl-4!>6. Also, Na- 

 ture, October :?, 1689, vol. xi„ pj). .^) 15-547.) 



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