132 BULLETIN OF THE 



would lose entirely their travelling motion, still retaining their rota- 

 tions. So also if their axes were equally inclined so as to bring 

 the points of impact on corresponding circles of latitude ; the limit- 

 ing case of which would be an impact on their poles of motion 

 in the line of their common axes of rotation.] Lastly if a rotating 

 inelastic body should meet a fixed resistance in the line of the 

 center of percussion, not only the translatory — but the rotary ve- 

 locity as well — would be entirely destroyed.* If we conceive a 

 molecule as consisting of a congeries of atoms having an orbital 

 revolution (analogous to a solar system), a very similar analysis 

 will apply to the cases of collision. 



It is very clear then that the device of storing up additional 

 kinetic energy in the form of internal rotation (or revolution; fails 

 utterly to reproduce the phenomena of motion exhibited by elas- 

 ticity. The resulting effects cannot be admitted as at all analogous ; 

 since the internal kinetic energy assumed is either wholly or 

 largely absorbed and exhausted by a single collision, and a second 

 impact can never reproduce the effects of a first one ; while elastic 

 force remains perpetual and unimpaired by constant action. 



Elasticity accordingly, equally with cohesion, is a fact of nature, 

 a property of matter, which can neither be interpreted by any form 

 of motion, nor resolved into any mechanical concept.f Those 

 therefore who would formulate the elements of things devoid of 



* Louis Poinsot. The latter portion of a series of mathematical discus- 

 sions under the general title — Questions dynamiques sur la Percussion des 

 Corps; published in Liouville's Journal de Mat hematiques for 1857: vol. 

 ii, pp. 281-308. 



f " Elasticity without an action e distanti — even between the adjoining 

 particles — is inconceivable. What is meant by elasticity ? Surely such 

 a constitution of the assemblage of particles as makes them recede from 

 each other." Prof. John Kobisox. (A System of Mechanical Philoso- 

 phy. 8vo. 4 vols. Edinburgh, 1882 : vol. nr, p. 139.) 



"An alteration of the form of a solid body is called a strain. In solid 

 bodies strain is accompanied with an internal force or stress ; those bodies 

 in which the stress depends simply on the strain are called 'elastic,' and 

 the property of exerting stress when strained is called elasticity. - - 



The general fact that strains or changes of configuration a*re accompanied 

 by stresses or internal forces, and that thereby energy is stored up in the 

 system so strained, remains an ultimate fact which has not yet been ex- 

 plained as the result of any more fundamental principle." Prof. J. Clerk 

 Maxwell. {Matter and Motion. 1876: chap, v, arts. 83, 84; pp. 70, 71. 



