We learn to talk, much about the same time that we learn to walk, but talking requires less muscular effort than walking, and makes generally less demand upon our powers. A man may talk a long while before he has done the equivalent of a five-mile walk; it is natural, therefore, that we should have had more practice in talking than in walking, and hence that we should find it harder to pay attention to our words than to our steps. Certainly it is very hard to become conscious of every syllable or indeed of every word we say; the attempt to do so will often bring us to a check at once; nevertheless we can generally stop talking if we wish to do so, unless the crying of infants be considered as a kind of _quasi_-speech: this comes earlier, and is often quite uncontrollable, or more truly perhaps is done with such complete control over the muscles by the will, and with such absolute certainty of his own purpose on the part of the wilier, that there is no longer any more doubt, uncertainty, or suspense, and hence no power of perceiving any of the processes whereby the result is attained—as a wheel which may look fast fixed because it is so fast revolving. {13} We may observe therefore in this ascending scale, imperfect as it is, that the older the habit the longer the practice, the longer the practice, the more knowledge—or, the less uncertainty; the less uncertainty the less power of conscious self-analysis and control. It will occur to the reader that in all the instances given above, different individuals attain the unconscious stage of perfect knowledge with very different degrees of facility. Some have to attain it with a great sum; others are free born. Some learn to play, to read, write, and talk, with hardly an effort—some show such an instinctive aptitude for arithmetic that, like Zerah Colburn, at eight years old, they achieve results without instruction, which in the case of most people would require a long education. The account of Zerah Colburn, as quoted from Mr. Baily in Dr. Carpenter’s “Mental Physiology,” may perhaps be given here. “He raised any number consisting of _one_ figure progressively to the tenth power, giving the results (by actual multiplication and not by memory) _faster than they could be set down in figures_ by the person appointed to record them. He raised the number 8 progressively to the _sixteenth_ power, and in naming the last result, which consisted of 15 figures, he was right in every one. Some numbers consisting of _two_ figures he raised as high as the eighth power, though he found a difficulty in proceeding when the products became very large. “On being asked the _square root_ of 106,929, he answered 327 before the original number could be written down. He was then required to find the cube root of 268,336,125, and with equal facility and promptness he replied 645.