stag asaiel 
— 
oe 
1883, ] 123 [Chase. 
two principal classes of maintained vibrations may be distinguished ; 
the more extensive class being that in which the magnitude and phase of 
the sustaining force depend in an approximately constant manner, upon the 
amplitude and phase of the vibration itself. The only case in which, ac- 
cording to (20), a steady vibration is possible, is when the complete 
value of x is zero, If any portion of the energy of cosmical masses is dis- 
sipated, ethereal energy must be proportionately increased. The ether 
accordingly becomes a ‘‘source of energy,’’ and although we are not yet 
able to see fully how the connection of this source with solar radiations is 
kept up, the equivalence of 0, to %, (Note 821) shows that it is kept up, 
through cyclical actions which cover a period of about 124 days, 
884. Virials of Wave Propagation. 
It has often been tacitly assumed that there is no actual radial oscillation 
in luminous radiation, like that of the atmospheric particles in the propaga- 
tion of sound-waves. In 1872 (Proc, Amer, Phil. Soc., xii, 394) I showed 
that the secondary centre of oscillation, on returning from the centre of 
linear oscillation towards the linear centre, is at of the extreme excur- 
sion. Hence the tangential virial of an oscillating sethereal particle (a), 
is 2 of the radial virial of the same particle (up ). More than five years after- 
wards (Phil. Mag. [5], iii, 453; iv, 209), Maxwell stated that the ratio of 
the virial velocity is 2%, but he gave no reason for his inference and none 
has yet been found among his unpublished papers. THis statement and 
mine are substantially identical, the only difference being that he looked to 
the relative mean momentum of the oscillating particles, while [ looked to 
their relative virials. 
9 
Pa = 1.8 LB 21. 
885. Zime-Relations of Inertia. 
The question of instantaneous action is still, and probably will long con- 
tinue to be, a mooted one. The most impressive form in which it has ever 
been presented, is Laplace’s statement that gravitating action requires a 
velocity which is more than 100,000,000 times as greatas the velocity of light, 
and that it may be assumed to be absolutely instantaneous at all distances, 
It is sometimes said that inertia is instantaneously overcome. This may, 
perhaps, be true in some sense, but we cannot know that it is so, until we 
know more than we have yet learned about the way in which velocity is 
transferred from one body to another. In general physical investigations 
the element of time, usually in the form of time-integrals, requires consid- 
eration whenever there is any change of motion. 
886. Correlation of Virials. 
Questions of kinetic unity and correlation are greatly complicated by 
differences of inertia and by the lack of generally recognized standards of 
comparison, If all forms of force are transmitted through ethereal interven- 
tion, all virials should be capable of representation in terms of ethereal 
mass and velocity. The velocity of luminous undulation then becomes ¢ 
