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! I would have plenty of games in the dark! This suggestion is more valuable than it seems at first sight. Men are naturally afraid of the dark; so are some animals. [Footnote: This terror is very noticeable during great eclipses of the sun.] Only a few men are freed from this burden by knowledge, determination, and courage. I have seen thinkers, unbelievers, philosophers, exceedingly brave by daylight, tremble like women at the rustling of a leaf in the dark. This terror is put down to nurses' tales; this is a mistake; it has a natural cause. What is this cause? What makes the deaf suspicious and the lower classes superstitious? Ignorance of the things about us, and of what is taking place around us. [Footnote: Another cause has been well explained by a philosopher, often quoted in this work, a philosopher to whose wide views I am very greatly indebted.] When under special conditions we cannot form a fair idea of distance, when we can only judge things by the size of the angle or rather of the image formed in our eyes, we cannot avoid being deceived as to the size of these objects. Every one knows by experience how when we are travelling at night we take a bush near at hand for a great tree at a distance, and vice versa. In the same way, if the objects were of a shape unknown to us, so that we could not tell their size in that way, we should be equally mistaken with regard to it. If a fly flew quickly past a few inches from our eyes, we should think it was a distant bird; a horse standing still at a distance from us in the midst of open country, in a position somewhat like that of a sheep, would be taken for a large sheep, so long as we did not perceive that it was a horse; but as soon as we recognise what it is, it seems as large as a horse, and we at once correct our former judgment.