220 
MR. J. LARMOR OR A DYRAMICAL THEORY OF 
view requires that the energy of chemical constitution shall be very great compared 
with the thermal energy ; but for this very reason our means of chemical decom¬ 
position are limited, so that onl}'- a part of that energy is experimentally realizable.* 
This being the case, the alteration produced by external disturbance in the state of 
steady internal motions of the molecule consists in the superposition on it of ver}’ 
slow free precessional motions, which have practically no influence on its higher free 
periods : t and this explains why change of temperature has no influence on the positions 
of the lines in a spectrum. As a gas at high temperature must contain molecules with 
all amounts of internal thermal energy from nothing upwards, we should on the other 
hand, on the ordinary gas-theory, expect both a shift of the brightest part of a spectral 
line when the temperature is raised, and also a widening of its diffuse margin. 
The ordinary encounters between the molecules will influence this thermal energ-v 
or energy of slow precessional oscillation, without disturbing the state of steady con¬ 
stitutive motion on which it is supei’posed, therefore without exciting radiation, which 
depends on more violent disturbances involving dissociative action. 
On this view the postulates of the Maxwell-Boltzmarn theorem on the distri¬ 
bution of the internal energy in gases would not obtain, for the thermal energy of 
the molecule would not be expressible as a sum of squares. The ratio of the specific 
heats in a gas must still lie between 1 and | ; but the nature of the similarity of 
molecular constitution in the more permanent gases, which makes the ratio of the 
total thermal energy to the translatory energy either -f or unity for most of them, 
AAmuld remain to be discovered. In those gases for wdiich the latter value obtains, the 
energy of precessional motion in the molecule would be negligibly small, involving 
small resultant angular momentum and possibly small paramagnetic moment. 
The necessity of a distinction such as that here drawn between the internal thermal 
energy and the energy of the vibratory disturbances of internal structure which 
maintain radiation, is well illustrated by the recent recognition (foreshadowed by 
Dulong and Petit’s researches on the law of cooling) and application by Dewar of 
the remarkable insulating power of a vacuum jacket as regards heat. If this 
distinction did not exist, both conduction and convection must ultimately depend on 
enclosed in a suitable massless case, coming into mutual encounter. We may imagine that neither of 
them has any internal heat; so that the internal energy of each is the minimum that corresponds to its 
steady gyrostatic momentum, and the axis of each gyrostat therefore keeps a fixed direction in space. 
The result of the encounter will be that the axis of each gyrostat acquires steady wobbling or free 
precessional motion, so that its internal energy is increased at the expense of the energy of translation 
of the atoms; but in this the simplest case there will be no unsteady vibration, such as could be radiated 
away. If howet^er there are also other types of momenta associated with the atom, for example if the 
case of the gyrostat is not massless, the encounter will leave vibrations about the new state of steady 
motion, which if of high enough period will lead to loss of energy by radiation. 
* Ideas somewhat similar to the above are advanced by Waterston in his classical memoir of 1815 on 
gas-theory, recently edited by Lord Rayleigh; ‘ Phil. Trans.’ (A), 1892, p. 51. 
t Cf. Thomson and Tait, ‘ Nat. Phil.’ § 345 xxiv. 
