tions for themselves. The mind forms an idea, and at first, after the fashion of the ancient Greek philosophers, it glorifies that idea and sets it in the seat of divinity. But presently comes the empirical method, which refuses authority to any idea unless it can stand the test of experiment, and prove that it corresponds with reality. Nowadays the thinker amasses his facts, and forms a theory to explain them, and then proceeds to try out this theory by the most rigid method that he or his critics can devise. If the theory doesn't "work" —that is, if it doesn't explain all the facts and stand all the tests it is thrown away like a worn-out shoe. So little by little a body of knowledge is built up which is real knowledge: which will serve us in our daily lives, which we can use as foundation-stones in the structure of our civilization.

By this method of research man is expanding his universe beyond anything that could have been conceived in the prescientific days. Hour by hour, while we work and play and sleep, the mind of our race is discovering new worlds in which our posterity will dwell. For uncounted ages man walked upon the earth, surrounded by infinite swarms of bacterial life of whose existence he never dreamed. The invisible rays of the spectrum beat upon him, and he knew nothing of what they did to him, whether good or evil. He lifted his head and saw vast universes of suns, in comparison with which his world was a mere speck of dust; yet to him these universes were globes or lanterns which some divinity had hung in the sky.

One of the most fascinating illustrations of how the mind runs ahead of the senses is the story of the planet Uranus, which, less than two hundred years ago, had never been beheld by the eye of man. A mathematician seated in his study, working over the observations of other planets, their motions in relation to their mass and distance, discovered that their behavior was not as it should be. At certain times none of them were in quite the right place, and he decided that this variation must be due to the existence of an unknown body. He worked out the problem of what must be the mass and the exact orbit of this body, in order for it to be responsible for the variations observed; and when he had completed these calculations, he announced to the astronomical world, "Turn your telescopes to a certain spot in the heavens at a certain minute of a certain night, and you will find a new planet of a certain size." And so for the first time the human senses

became aware of a fact, which by themselves they might not have discovered in all eternity.

Now, the importance of exact knowledge concerning a new planet may not be apparent to the ordinary man; but if the thing which is discovered is, for example, an unknown ray which will move an engine or destroy a cancer, then we realize the worthwhileness of research, and the masters of the world's commerce are willing to give here and there a pittance for the increase of such knowledge. But men of science, who have by this time come to a sense of their own dignity and importance, understand that there is no knowledge about reality which is useless, no research into nature which is wasted. You might say that to describe and classify the fleas which inhabit the bodies of rats and ground-squirrels, and to study under the microscope the bacteria which live in the blood of these fleas that this would be an occupation hardly worthy of the divinity that is in man. But presently, as a result of this knowledge about fleas and flea diseases being in existence and available, a bacteriologist discovers the secret of the dread bubonic plague, which hundreds of times in past history has wiped out a great part of the population of Europe and Asia.

Mark Twain tells in his "Connecticut Yankee" how his hero was able to overcome the wizard Merlin, because he knew in advance of an eclipse of the sun. And this was fiction, of course; but if you prefer fact, you may read in the memoirs of Houdin, the French conjurer, how he was able to bring the Arab tribes into subjection to the French government by depriving the great chieftains of their strength. He gathered them into a theatre, and invited their mighty men upon the stage, and there was an iron weight, and they were able to lift it when Houdin permitted, and not to lift it when he forbade. These noble barbarians had never heard of the electro-magnet, and could not conceive of a force that could operate through a solid wooden floor beneath their feet.

Such things, trivial as they are, serve to illustrate the difference between ignorance and knowledge, and the power which knowledge gives. The man who knows is godlike to those who do not know; he may enslave them, he may do what he pleases with their lives, and they are powerless to help themselves. Anyone who would help them must begin by giving them knowledge, real knowledge. There is no such thing as freedom without knowledge, and it must be the best

knowledge, it must be new knowledge; he who goes against new knowledge armed with old knowledge is like the Chinese who went out to meet machine-guns with bows and arrows, and with umbrellas over their heads.

Once upon a time knowledge was the prerogative of kings and priests and ruling castes; but this supreme power has been wrested from them, and this is the greatest step in human progress so far taken. "Seek and ye shall find," is the law concerning knowledge today. "Knock, and it shall be opened unto you. In this, my Book of the Mind, I say to you that knowledge is your priceless birthright, and that you should repudiate all men and all institutions and all creeds and all formulas which seek to keep this heritage from you. Beware of men who bid you believe something because it is told you, or because your fathers believed it, or because it is written in some ancient book, or embodied in some ancient ceremonial. Break the chains of these venerable spells; and at the same time beware of the modern spells which have been contrived to replace them! Beware of party cries and shibboleths, the idols of the forum, as Plato called them, the prejudices which are set as snares for your feet. Beware of cant-that paraphernalia of noble sentiments, artificially manufactured by politicians and newspapers for the purpose of blinding you to their knaveries. Remember that you live in a world of class conflicts; at every moment of your life your mind is besieged by secret enemies, it is exposed to poison gas-clouds deliberately released by people who seek to make use of you for purposes which are theirs and not yours. In the fairy-tales we used to love, the hero was provided with magic protection against the perils of those times; but what hero and what magic will guard the modern man against the propaganda of militarism, nationalism, and capitalist imperialism?

The mind is like the body in that it can be trained, it can be taught sound habits, its powers can be enormously increased. There are many books on mind and memory training, some of which are useful, and some of which are trash. There is an English system widely advertised, called "Pelmanism," of which I have personally made no test, but it has won endorsements of a great many people who do not give their endorsements lightly.

This is the subject of applied psychology, and just as in medicine, or in law, or in any of the arts, there is a vast amount

of charlatanry, but there is also genuine knowledge being patiently accumulated and standardized. When the United States government had to have an army in a hurry it did not make its millions of young men into teamsters or aviators at random. It used the new methods of determining reaction times, and testing the coordination of mind and body. Recently I visited the Whittier Reform School in California, where delinquent boys are educated by the state. A boy had been set to work in the tailor shop, and it had been found that he was unable to make the buttons and the buttonholes of a coat come in the right place. For nine years the state of California, and before it the state of Georgia, had been laboring to teach this boy to make buttons and buttonholes meet; the effort had cost some five thousand dollars, to say nothing of all the coats which were spoiled, and all the mental suffering of the victim and his teachers. Finally someone persuaded the state of California to spend a few thousand dollars and install a psychological bureau for the purpose of testing all the inmates of the institution; so by a half hour's examination the fact was developed that this boy was mentally defective. Although he was eighteen years old in body, his mind was only eight years old, and so he would never be able to achieve the feat of making buttons and buttonholes meet.

This is a new science which you may read about in Terman's "The Measurement of Intelligence." By testing normal children, it is established that certain tasks can be performed at certain ages. A child of three can point to his eyes, his nose and his mouth; he can repeat a sentence of six syllables, and repeat two digits, and give his family name. Older children are asked to look at a picture and then tell what they saw; to note omissions in a picture, to arrange blocks according to their weight, to arrange words into sentences, to note absurdities in statements, to count backwards, and to make change. Children of fifteen are asked to interpret fables, to reverse the hands of a clock, and so on. Of course there are always variations; every child will be better at some kinds of tests than at others. But by having a wide variety, and taking the average, you establish a "mental age" for the childwhich may be widely different from its physical age. You may find some whose minds have stopped growing altogether, and can only be made to grow by special methods of education. Enlightened communities are now conducting separate

CHAPTER XVII

THE CONDUCT OF THE MIND

(Concludes the Book of the Mind with a study of how to preserve and develop its powers for the protection of our lives and the lives of all men.)

Someone wrote me the other day, asking, "When is the best time to acquire knowledge?" I answer, "The time is now." It is easier to learn things when you are young, but you cannot be young when you want to be, and if you are old, the best time to acquire knowledge is when you are old. It is true that the brain-cells seem to harden like the body, and it is less easy for them to take on new impressions; but it can be done, and just as Seneca began to learn Greek at eighty, I know several old men whom the recent war has shaken out of their grooves of thought and compelled to deal with modern ideas.

But if you are young, then so much the better! Then the divine thrill of curiosity is keenest; then your memory is fresh, and can be trained; your mind is plastic, and you can form sound habits. You can teach yourself to respect truth and to seek it, you can teach yourself accuracy, open-mindedness, flexibility, persistence in the search for understanding.

First of all, I think, is accuracy. Learn to think straight! Let your mind be as a sharp scalpel, penetrating unrealities and falsehoods, cutting its way to the facts. When you set out to deal with a certain subject, acquire mastery of it, so that you can say, "I know." And yet, never be too sure that you know! Never be so sure, that you are not willing to consider new facts, and to change your way of thinking if it should be necessary. I look about me at the world, and see tigers and serpents, dynamite and poison gas and forty-two centimeter shells-yet I see nothing in the world so deadly to men as an error of the mind. Look at the mental follies about you! Look at the prejudices, the delusions, the lies deliberately maintained-and realize the waste of it all, the pity of it all!

Every man, it seems, has his pet delusions, which he hugs