The reason we cannot do this always is because when we walk naturally the steps taken by our right and left feet are not of equal length. This difference in the length of the steps is due to the fact that our legs are never exactly the same length. We think of them generally as of the same length, but they are not, and this will be proven if you measure them accurately. Now, then, the longer of the legs will always take a longer step than the shorter one, and so, if our eyes are shut, we walk in circles, unless we have something to guide us. When we walk with our eyes open, we are able to overcome the tendency to walk in circles, because our eyes help the brain to direct the legs on a straight course. Another reason which affects the matter is that our eyes are very necessary in keeping our bodies balanced on our feet, and it is very difficult to learn to keep the body balanced with the eyes closed. Now, when your eyes are closed and you attempt to walk in a straight line your body balances from one side to the other, and this fact, coupled with the first reason given, makes your course irregular. But, say you, the man on the tight-rope has his eyes bandaged and he walks a very straight line. Yes; but remember that he has a straight tight-rope to guide him, and all he needs is to maintain his balance. One can learn to walk in a straight line with the eyes closed, but it takes a good deal of practice, as you will learn if you try. Why Can’t We Sleep with Our Eyes Open? We cannot sleep with our eyes open, because to be asleep involves losing control of most of the functions of the body. When we sleep the brain sleeps also. Perhaps it would be stated more clearly to say that we cannot sleep while the part of the brain which controls our activities is awake. There is a part of the brain which has the power to open our eyes, i. e., lift the eyelids, and when that portion of the brain ceases to exercise its power to keep the eyes open, they go shut. Even when we are awake that part of our brain cannot keep our eyes from winking, because there is another part of the brain which sees to it that our eyes wink every so often. This is done for the purpose of washing the eye-ball, and is the answer to another of your questions which is given in another place in this book. When the engineer at the electric light plant shuts off the power all the lights go out, and when you go to sleep you automatically shut off the power that opens your eyes, and the eyes are shut. The brain is asleep also, and if it is not completely asleep, you are restless. Why Do Our Eyes Sparkle When We Are Merry? If you should watch very closely the eyes of a merry person when you see them sparkle you would probably notice that the eyelids move up and down more often under such conditions than ordinarily, and if you know what moving the eyelids up and down in front of the pupil of the eye does, you will have your answer.