Since, however, the ob server is not conscious of his own translatory motion FIG.
Highest temperatures at our command it is small compared with the energy of translatory motion, but as the temperature increases, it must ultimately gain the upper hand, and if there is anywhere such a temperature as that of several million degrees, the greater part of the total energy of a body will be outside the atom and molecular motion ultimately becomes negligible compared with it.
A limit to homogeneity of radiation is ultimately set by the so-called Doppler effect, which is the change of wave-length due to the translatory motion of the vibrating molecule from or towards the observer.
In the case of hydrogen rendered luminous in a vacuum tube we may put approximately u equal to 2000 metres per second, if the translatory motion of the luminous molecules is about the same as that at the ordinary temperature.
He finds a remarkable agreement between the theoretical and experimental values, which it would be important to confirm with the more suitable instruments which are now at our disposal, as we might in this way get an estimate of the energy of translatory motion of the luminous molecules.