r 205 ] 
IX. A Dijimmical Theory of the Electric and Luminiferous Medium .— 
Part III. Relations ivith Material Media. 
By Joseph Larmor, F.R.S., Fellow of St. Johns College, Cambridge. 
Received April 21, 1897,—Read May 13, 1897. 
Contents. 
{The numbers refer to sections.) 
Page 
Introductory (1, 2).206 
Consideration of a gyrostatic model of the rotational a3ther : its limitations (3, 4) . . 209 
Illustration by an elastic solid possessing intrinsic strain; the usual notion of propaga¬ 
tion by a medium is too narrow (5, 6).211 
Continuous Eether contrasted with molecular matter: the notion of mechanical as 
distinct from total energy (7-10).215 
Kinetic constitution of a molecule; its influence on the kinetic theory of gases (11, 12) 219 
General equations of the gethereal field, with stagnant aether and moving matter: 
various applications: influence of motion through the aether on the dimensions of 
bodies (13-16).221 
Consideration of a complication connected with permanent co-existence of a magnetic 
field and an electrostatic field (17).230 
Relations of inductive capacity and optical refraction to density (18-22). 232 
Generalized theory of optical dispersion, the molecular vibi’ations taking place about 
states of steady motion (23-33). 236 
Optical deviation by thin opaque prisms (34). 247 
The mechanical tractions on dielectric interfaces : and the mechanical bodily forcive 
(35-39). 248 
Interpretation of Maxwell’s theorem of a representative stress (40). 254 
The regular local molecular forcive in an excited dielectric: its expi’ession as a stress- 
system : examples of the principle of mutual compensation of molecular forcives (41-47) 254 
The mutual compensation of molecular agencies: mechanical and non-mechanical 
energy : relation to thermodynamics, available and degraded energy: j^hysical basis 
of the idea of temperature (48-51). 260 
Application to fluids: Laplace’s intriusic pressure : law of osmotic pressure : laws of 
chemical equilibrium (52-62) 266 
The electric potential-differences established by steady finite diffusion (63). 277 
Critique of von Helmholtz’s investigation of stresses in polarized media : the phenomena 
of electrostriction not directly related to mechanical stress (64-68) ....... 280 
Conservation of energy in the electrodynamic field : limited validity of Potnting’s 
principle (69, 70). 285 
The nature of paramagnetism and diamagnetism, as indicated by their temperature 
relations (71, 72). 286 
Mechanical reaction of radiation, reconsieiered (73,74). 289 
9.2.S8 
