enters) usurps the position of
. Now
also affects the flow of time, hence affects the rate of vibration of atoms (as in the Einstein shift-effect); and so we can detect variations in the value of the potential
from place to place through the medium of spectroscopic observations. But when we undertake our observations from a Galilean frame (the earth will do in this case), we notice that lines in the spectra of the most distant nebulæ occupy positions practically identical with those of terrestrial sources, whence we may conclude that as far as the telescope can explore, the value of
remains approximately constant. As for the velocities of the stars, they would be affected by the values of all the