Time advances: facts accumulate; doubts arise. Faint glimpses of truth begin to appear, and shine more and more unto the perfect day. The highest intellects, like the tops of mountains, are the first to catch and to reflect the dawn. They are bright, while the level below is still in darkness. But soon the light, which at first illuminated only the loftiest eminences, descends on the plain, and penetrates to the deepest valley. First come hints, then fragments of systems, then defective systems, then complete and harmonious systems. The sound opinion, held for a time by one bold speculator, becomes the opinion of a small minority, of a strong minority, of a majority of mankind. Thus, the great progress goes on.