On Material Molecules and the Etlierial Medium. 261 
by the symmetry of the arrangement of the etheria 
particles. 
Hence from (12), (13), (14), and (15) 
d'^u . ^\ d'^u r,\ d% 
2E ^ (^^ div\ 
dx \dy dz ) 
Now, if the vibrations of the ether be transversal to the 
direction of propagation, 
du dv diu ^ 
dx dy dz ~ ' 
Hence in this case 
Hence putting E + S = A we have 
dx dy dz 
. ( dht d'^u dht ] 
= ^{m-' d^^"- d?\ ■ ■ ■ ■ 
Again, if m' be the mass of one of the material molecules, 
and rfr the law of the action of the molecules on the ether, 
=: m'l{fr'(x' -x)} 
= 7)1 2 fr . }i say 
d^_e 
dy 
d'Xj: 
dz 
= — m 
{^fr'h'!/\ . . , . (18) 
'M l-A'^''^'} • • • • (18*) 
Now, let us take as the typical case of a biaxal crystal 
