THE SIZE OF ATOMS. 185 



in cubic order, and each particle to attract its 

 six nearest neighbours, with a force varying 

 directly as the excess of the distance between 

 them, above a certain constant line (the length of 

 which is to be chosen, according to the degree 

 of compressibility possessed by the elastic solid, 

 which we desire to represent by a crowd of 

 mutually interacting molecules). If you suppose 

 particles of real matter arranged in the cubic order, 

 and six steel wire spiral springs, or elastic india- 

 rubber bands, to be hooked on to each particle 

 and stretched between it and its six nearest 

 neighbours, the postulated force may be produced 

 in a model with all needful accuracy ; and if we 

 could but successfully wish the theatre of the 

 Royal Institution conveyed to the centre of the 

 earth and kept there for five minutes, I should 

 have great pleasure in showing you a model of an 

 elastic solid thus constituted, and showing you 

 waves propagated through it, as are waves of 

 light in the luminiferous ether. Gravity is the 

 inconvenient accident of our actual position which 

 prevents my showing it to you here just now. 



