As you throw open the window to see what kind of a day it is going to be, whether fair, or cloudy, or rainy, cool or warm, you draw your conclusions from the appearance of sky and air, but in doing that you are entering another field covered by another branch of science and included in our little library--meteorology, or the realm of the air--and you may be sure that the correctness of the conclusions that you draw from the aspect of the clouds and the feeling of the air will be greatly increased, not only in certainty, but also in interest, if you read what the students of this subject have learned about the laws and the mysteries of the rains, clouds, cyclones, barometric pressures, great winds and genial breezes, great storms and little storms; in short, the whole wonderful science of the atmosphere, that invisible, yet powerful kingdom of the air, which we are just beginning to annex to our world of activities without regard to what its natural occupants, the birds, think of such an invasion.

Now you leave the window to begin making your morning ablutions. You turn on a faucet and take a drink, or plunge hands and face into the refreshing liquid, so cool, lively, and invigorating. But a bird or any four-footed animal may find just as keen physical enjoyment in the touch and taste of the water as you do. You, however, because you are a thinking being, possess a source of enjoyment from the touch and appearance of the water that is not open to those humbler creatures, and that source of enjoyment springs from the principles and facts of another branch of science which the mere sight of the running water may call to mind if you have caught the spirit of these books--the science of chemistry, whose early history is filled with that irresistible kind of romance that pertains to the search for Eldorado, or the strivings of the human spirit after the powers of magic; for the realm of chemistry was once a kind of semi-scientific dreamland, wherein the "alchemists" delved at the same time for the "philosopher's stone" which was to turn base metal into gold, and for the wand of the magician which would give to its possessor the boundless gratifications of a Faust. Water is no mystery to the lower animals, but it is a great mystery even yet to the highest ones--ourselves--because we have been enabled to analyze it. You cannot look at it pouring from the faucet, and sparkling into bubbles, without recalling the fact that it is composed of two invisible, silent gases, and that chemistry tells us not only how to make the water disappear by taking those gases apart, but also how to form new water by making the two gases combine. The mystery is--why should this be so? It is a captivating question, and the business of the book on chemistry is to give you all possible light on the solution of that question, and others of a like nature. You will find, too, that the very latest chemistry has, strangely enough, discovered a sort of justification for the extravagant expectations of the ancient alchemists, by finding a way in which one substance may actually change, or be changed, into another, different substance--one "element" taking the form of another "element"--and also by getting clues to the existence of marvelous locked-up energies in matter, the release of which would give man control over powers that could properly be called "magical."

After finishing your toilet, with all the suggestions and remembrances of chemical science that it has produced, you start to quicken the circulation of your blood by catching up a pair of dumb-bells, or Indian clubs, or by pulling elastic cords, or banging a leather ball with your fists, as if you meant to go in for the championship of the world. Now, what taught you the value of such exercises? You are still on the ground of science, and you are practically demonstrating the principles of another of its branches--the science of health, or hygiene, which is a part of the subject of medicine, taken in its broadest signification, for, as the volume on that subject will assure you, the greatest service that this science can render to mankind is in teaching us the laws of our physical existence, and indicating, directly or indirectly, how all the functions of the body may be kept in the best working order by proper attention and exercise. You will find such things pointed out in the several sciences that deal with the body, such as physiology and medicine.

While you are making the leather ball strike the ceiling with resounding whacks, your dog, excited by the inspiring noise, bursts into the room, and interrupts your exercise with his enthusiastic morning greetings, expressed as energetically by his wagging tail as by his joyous barks and licks, all anticipatory of a lively morning run. He brings immediately into your mind the thought of still another division of science--zoölogy--to which you will devote many pleasant half-hours of reading, for it is full of most entertaining matter, as well as of matter calculated to awaken profound and useful thought concerning the relations of the many different members of the animal world to one another, and especially to their head and chief, man, to whom the supervision of the whole was, according to the Bible story, originally committed. Familiar as your dog may be to you, there are a hundred particulars of his family relationships, his descent from wild ancestors, etc., which can only become known to you through the studies that have been devoted to the science of zoölogy by curious-minded investigators from the times of Aristotle and Pliny down to our own day, when we have seen an ex-President of the United States wandering adventurously through some of the remotest portions of the inhabited globe, seeking fresh knowledge of, and personal acquaintance with, the rarer kinds of wild animals, and hunting down in their native wilds great beasts which the Cæsars used to admire from the security of the imperial seat, high above the bloody sands of the Roman arenas. And this modern ruler, after having laid down the political power intrusted to him by fellow citizens, found no occupation so attractive as that of adding something to the growing stores of science.

Next, your stomach, awakened to its wants and needs by the restored circulation resulting from your lively exercises, reminds you of what will be at the same time a pleasure and a means of sustained strength for body and mind, your breakfast. Breakfast properly comes under the supervision of the science of physiology. It is also suggestive of mechanics and physics, since it has to do with the stoking of the furnace that keeps the bodily engine up to its work. Here you are face to face with a branch of science which you could no more safely neglect than an engineer or a fireman could neglect to learn the elements and principles underlying his critically important occupation. One of the first sciences to be systematically developed was that of man's body, including its structure, or anatomy, and its functioning, or internal action, physiology. You will find that correct ideas on these subjects were slow in being developed, yet even in the most ancient times men were shrewd and wise enough to understand the importance of knowing something about their own bodies, in order to be able to take proper care of them, and to deal with wounds and sickness.

It was an old saying that "the proper study of mankind is man." But that is a study which has two main branches. The first covers the subjects of physiology, anatomy, medicine, etc., while the second relates to that even more intimate part of ourselves which has ever been a fascinating mystery, and which we call the mind, or sometimes the soul. This is the theme of the science of psychology, whose name comes from that delicate, inscrutable spirit, Psyche, the Soul, which plays like a flitting sunbeam through the magical atmosphere of Greek mythology. Now, this subtle and exquisite science, often more poetic and mystic than scientific in its original character, presents itself in its more sober and practical dress to you as soon as, having finished your breakfast and prepared your bodily energies for the day's work, you begin to meditate on the problems of the day opening before you.

When you went to bed, perhaps your mind was agitated by some important matter of business through whose intricacies you could not clearly see your way. You turned and tossed on your pillow, and stated and restated the facts and arguments and lines of reasoning, but all the while they became more obscure and entangled until at last, in sheer exhaustion, you fell into a troubled sleep. But this morning, to your immense surprise and gratification, without any effort on your part, and while you are occupied with other things--putting on your clothes, hitting the ball, playing with the dog, eating your bacon and eggs, or what not--suddenly the elusive clue or solution, so vainly sought the night before, presents itself plain before you. In an instant, in the twinkling of an eye, the troublesome problem is solved, as easily and naturally as water runs down hill, and you are provoked at yourself for having been so dull and stupid as not to see it all before. But not so fast! You were stupid, to be sure, but it was not your mind's fault as you are now disposed to think, but the trouble lay in your physical fatigue. You were driving your brain too long without refreshment, and it became like an engine whose oil cups are empty. It could not receive and report the impressions of thought.