'Questions of fact,' observes Pascal, in his celebrated 'Provincial Letters,' 'are only to be determined by the senses. If what you assert be true, prove it to be so; if it be not, you labour in _vain_ to induce belief. All the authority in the world cannot enforce or alter belief as to facts; nothing can possibly have power to cause that not to be which actually _is_.'* A remarkable instance of the verification of what was assumed to be is related of Pascal by Goodrich. 'Pascal was a philosopher even in childhood. At a very early age he was taught the ten commandments. For several days after, he was observed to be measuring the growth of a blade of grass. When asked the meaning of this, he replied, "The fourth commandment says, 'Six days shalt thou labour, but the seventh is the Sabbath in which thou shalt do no work.' Now I wished to ascertain if nature obeyed this great law, and therefore measured the grass, to see if it grew as much on Sunday as on other days." '** 'We are informed,' says Beattie, 'by Father Malebranche, that the senses were at first as honest faculties as one could desire to be endued with, till after they were debauched by original sin; an adventure from which they contracted such an invincible propensity to cheating, that they are now continually lying in wait to deceive us. But there is in man, it seems, a certain clear-sighted, stout, old faculty, called _reason_, which, without being deceived by appearances, keeps an eye upon the rogues, and often proves too cunning for them.'*** * Letter xviii. ** Fireside Education, p. 89. *** Essay on Truth, p. 105. Though it is so abundantly obvious that the evidences of our senses, internal and external, are, in effect, the sources of all certainty, yet we are not warranted in rejecting, as mere hypothesis, every theory which we cannot at once corroborate. When Euler remarked of his new law of arches, 'This will be found true, though contrary to all experience'--when Gall exclaimed of his new philosophy of the sensorium, 'This is true, though opposed to the philosophy of ages'--they expressed demonstrable truths hidden from the multitude. They announced new generalisations to man. New truths are commonly found to be old unnoted experiences, for the first time subjected to classification, and presented in a scientific form. To me it seems almost in vain to urge men to notice facts who have never noticed themselves. The truest standards of certainty arise from individuality of retrospection. An intelligent man is, himself to himself, the measure of all things in the universe.