"For no truth contrary to current opinion, even though demonstrable with almost geometrical certitude, can ever, unless capable of material proof, be suddenly established. Time, custom, and example alone are able to give it a solid foundation. Men accustom themselves to belief, as to everything else; indeed they generally believe from habit, and not from any sentiment of conviction within their minds. At length it happens that the once-questioned truth is taught to children, and is universally accepted. People are then astonished that it was ever unknown to them, and they ridicule their ancestors and contemporaries for the ignorance and obstinacy they manifested in opposing it. The greater and more important the new truths, so much the greater will be the difficulty of procuring acceptance for them; since they will overthrow a proportionately large number of opinions hitherto rooted in the minds of men. For even acute and practised intellects do not easily enter into the spirit of reasonings which demonstrate new truths that exceed the limits of their own knowledge; especially when these are opposed to beliefs long established within them. Descartes, in his geometrical discoveries, was understood by but very few of his contemporaries. It was the same with Newton. Indeed, the condition of men pre-eminent in knowledge is somewhat similar to that of literary men, and 'savants' who live in places innocent of learning. The latter are not deservedly esteemed by their neighbours; the former fail to be duly appreciated by their contemporaries. Both are often despised for their difference in manner of life and opinions from other men, who neither do justice to their ability nor to the writings they put forth in proof of it. "There is no doubt that the human race makes continual progress in knowledge. As a body, its march is slow and measured; but it includes certain great and remarkable minds which, having devoted themselves to speculation about the sensible or intelligible phenomena of the universe, and the pursuit of truths, travel, nay sometimes flash, to their conclusions in an immeasurably short space of time. And the rapid progress of these intellects stimulates other men, who hasten their foot-steps so as to reach, later on, the place where these superior beings rested. But not until the lapse of a century or more do they attain to the knowledge possessed by an extraordinary intellect of this kind.