1901 - 2 .] Lord Kelvin on Molecular Dynamics of a Crystal. 213 
each case corresponds to the least distance between neighbours at 
which next-nearests are beyond range of mutual force. All the 
diagrams here reproduced were drawn first on a large scale on 
squared paper for use in the calculations from (7 ) ; which included 
accurate determinations of the maximum and minimum values of 
w and the corresponding distances between nearest neighbours in 
each assemblage. The corresponding densities, given in the last 
column of the following table of results, are calculated by the 
formula J 2/A. 3 for assemblage I., and 2J2JX 8 for assemblage II. ; 
“ density ” being in each case number of atoms per cube of the 
unit of abscissas of the diagram. This unit is (§ 14) equal to the 
diameter of the atom. For simplicity we assume the atom to be 
an infinitely hard ball exerting (§ 13) on neighbouring atoms, not 
