Take the case of moving a heavy mass; if he takes too long a lever, he will waste his strength; if it is too short, he will not have strength enough; experience will teach him to use the very stick he needs.  This knowledge is not beyond his years.  Take, for example, a load to be carried; if he wants to carry as much as he can, and not to take up more than he can carry, must he not calculate the weight by the appearance?  Does he know how to compare masses of like substance and different size, or to choose between masses of the same size and different substances?  He must set to work to compare their specific weights.  I have seen a young man, very highly educated, who could not be convinced, till he had tried it, that a bucket full of blocks of oak weighed less than the same bucket full of water.

All our senses are not equally under our control.  One of them, touch, is always busy during our waking hours; it is spread over the whole surface of the body, like a sentinel ever on the watch to warn us of anything which may do us harm.  Whether we will or not, we learn to use it first of all by experience, by constant practice, and therefore we have less need for special training for it.  Yet we know that the blind have a surer and more delicate sense of touch than we, for not being guided by the one sense, they are forced to get from the touch what we get from sight.  Why, then, are not we trained to walk as they do in the dark, to recognise what we touch, to distinguish things about us; in a word, to do at night and in the dark what they do in the daytime without sight?  We are better off than they while the sun shines; in the dark it is their turn to be our guide.  We are blind half our time, with this difference:  the really blind always know what to do, while we are afraid to stir in the dark.  We have lights, you say.  What always artificial aids.  Who can insure that they will always be at hand when required.  I had rather Emil’s eyes were in his finger tips, than in the chandler’s shop.

If you are shut up in a building at night, clap your hands, you will know from the sound whether the space is large or small, if you are in the middle or in one corner.  Half a foot from a wall the air, which is refracted and does not circulate freely, produces a different effect on your face.  Stand still in one place and turn this way and that; a slight draught will tell you if there is a door open.  If you are on a boat you will perceive from the way the air strikes your face not merely the direction in which you are going, but whether the current is bearing you slow or fast.  These observations and many others like them can only be properly made at night; however much attention we give to them by daylight, we are always helped or hindered by sight, so that the results escape us.  Yet here we use neither hand nor stick.  How much may be learnt by touch, without ever touching anything!