It is necessary at first, that I repeat a truth which I have already said: that intellectual nature is always one and the same, whereas physical nature varies, changes unceasingly with time and place, and is modified in a thousand ways according to circumstances. Now, it is this latter nature which gives the form, that is to say, which renders sentient and particular that which the former gives to it as universal and intelligible; so that its aptitude more or less great, in receiving and in working upon the intelligence, can make the things which are more homogeneous in their principle appear more dissimilar in their effect. I will give a proof. Whilst the most profound obscurity covered Europe, whilst ignorance spread on all sides its baleful veils, there were found, however, at long intervals, certain privileged men, who, raising themselves above these thick vapours, came to grasp certain faint glimmerings of the light shining always above them. These men possessors of such rare gifts, would have indeed wished to communicate them to their contemporaries, but if they imprudently opened their mouths, the blind and fanatic horde which surrounded them cried out forthwith against the heretic, the magician, the sorcerer, and conducted them to torture as the price of their lessons.[181] After several sorry examples, these men, having become prudent, assumed the part of silence by retiring into monasteries or hermitages, studying Nature there in quietude, and profiting alone by their discoveries. If certain ones still dared to speak, it was by borrowing the style of religion, or history, diverting from the ordinary sense certain ideas received, explaining themselves by enigmas, or by figures, which, when necessary, they were able to explain as they wished.