John Tyndall

Invective may be a sharp weapon, but overuse blunts its edge. Even when the denunciation is just and true it is an error of art to indulge it too long.

Knowledge once gained casts a light beyond its own immediate boundaries.

Life is a wave, which in no two consecutive moments of its existence is composed of the same particles.

The brightest flashes in the world of thought are incomplete until they have been proven to have their counterparts in the world of fact.

The brightest flashes in the world of thought are incomplete until they have been proved to have their counterparts in the world of fact.