152 Chapter 10
Still others offered various attempts to synthesize the Newtonian emission theory with
some kind of medium, most notably Johann II Bernoulli, Euler ’ s childhood friend and son
of his Basel mentor. In 1736, the younger Johann submitted to the Paris Acad é mie a physi-
cal and mathematical investigation into the propagation of light. Johann II considered the
ether to be filled with infinitely many tiny vortices, interspersed with hard, small particles
that are sent into longitudinal vibrations about their equilibrium positions as a result of
compression transmitted through the vortices. This resulted in what he called a “ light fiber ”
( fiber lumineuse ) stretching along the line of particles, its luminosity propagated from one
particle to the next. The first particle in the series determined the way the light would
travel down the fiber, in which particles much larger or smaller than the first would be
unable to follow the traveling motion of the light ray. Bernoulli compared this process to
the resonance of a string instrument in sympathetic vibration, responding to vibrations of
another nearby string tuned at the same pitch.^2Figure 10.1
Huygens ’ s principle, showing the constructive interference of pulse fronts along the line DCEF , from his Trait é
de la lumi è re (1690).