Physics

In the ether thus constituted there are therefore propagated
transverse vibrations, regarding which all experiments in optics
furnish very precise information. The amplitude of these vibrations is
exceedingly small, even in relation to the wave-length, small as these
last are. If, in fact, the amplitude of the vibrations acquired a
noticeable value in comparison with the wave-length, the speed of
propagation should increase with the amplitude. Yet, in spite of some
curious experiments which seem to establish that the speed of light
does alter a little with its intensity, we have reason to believe
that, as regards light, the amplitude of the oscillations in relation
to the wave-length is incomparably less than in the case of sound.