SOME VIEWS ON LORD KELVIN'S WORK 425 



the definite groundwork presented for the ether in his own 

 compressible elastic solid theory of 1888, and for matter simply 

 a substance acting on the ether with a force depending on the 

 distance. The introduction of eighteenth-century views of 

 atoms as mere centres of force is of course merely tentative, 

 as explained in Appendix A to the Baltimore Lectures, where 

 the necessary relations of atoms and ether depending on their 

 relative motion is discussed. As a simplest case, for the atom 

 of matter, Lord Kelvin assumes a spherical nucleus occupying 

 a portion of space without excluding the ether. The atom 

 produces by its action on the ether condensation and rarefaction 

 at different distances from its centre, the total quantity of ether 

 within its boundary being the same as in an equal volume of 

 space free of matter, so that the outside ether is undisturbed. 

 In such an atom, the conditions of free mobility through space 

 are fulfilled for velocities less than the velocity of light. Beyond 

 this the essential quality of the atom is its positive electrification, 

 and the law of force experienced by an electron placed anywhere 

 within it. The latter is taken the same as the law of force due 

 to a uniform distribution of positive electricity within the 

 boundary of the atom. That the material nucleus may have 

 additional qualities of its own is a condition derived no doubt 

 from the failure of the vortex atom theory. Differences in 

 quality between atoms may be due in part at least to the 

 quantum numbers of the electrons required to neutralise each 

 atom. Lord Kelvin, however, expressly disclaims the idea that 

 any theory of matter can be founded merely on the interaction 

 of positive nuclei with electrons. " We might be tempted to 

 assume that all chemical action is electric, and that all varieties 

 of chemical substance are to be explained by the numbers of 

 the electrons required to neutralise an atom or set of atoms ; 

 but we can feel no satisfaction in this idea when we consider 

 the great and wild variety of quality and affinities manifested 

 by the different chemical elements. It is possible that the 

 differences of quality are to be wholly explained in merely 

 Boscovichian fashion by differences in the laws of force between 

 the atoms, and may not imply any differences in the numbers 

 of electrons constituting their quantums." As to the influence 

 of radiation, the atom is assumed to be unmoved by ether 

 waves, which, however, set electrons vibrating about their 

 positions of stable equilibrium within the atom. 



