moves; and velocity, or rate at which it moves : and these must always depend upon the force or forces by which the motion is produced. The principal producers of motion are the common natural forces, such as heat, gravitation, electricity, and animal or muscular force. We see heat employed in the various forms of the steam engine; gravitation, in the watermill and the pendulum; electricity, in the telegraph; and muscular force, in the work done by man and the inferior animals. Machines are not, as some young persons fancy, producers of motion; they are but appliances for altering and applying force. Much thought and effort have been wasted in the endeavour to invent a machine that should set itself in motion, and then go on for ever. Men have, with wonderful ingenuity, invented means for employing the forces of nature and for reducing friction, but man can no more create force than he can create matter. And, what is perhaps more wonderful still, it appears that force, like matter, is never really lost or exhausted. Its form may change,lost or used up here, it exists elsewhere; and in the good time of the Omnipotent Ruler, it comes forth again to do the work He has ordained it. Home Exercise.-1. Define motion, velocity, force, detect, obviously, and heat. 2. Show that motion and rest are equally natural. 3. Give the leading producers of motion. SHAKSPEARE makes one of his characters to say, "I can call spirits from the vasty deep," when the speaker is met by the reply," But will they come when you so do call?" So it is with theory. Any one may say that he can form theories about all things in heaven above, the earth beneath, or the waters under the earth. But the important question is, can he prove his theories when he has formed them? You, for instance, may have adopted the theory that the moon is made of green cheese. Well, so far you may be allowed to retain your theory; but before any sensible person accepts it, you will be asked for your proofs, and if you cannot supply them, you may be left alone with your belief. Again, some persons think, or pretend to think, that it is undignified to demonstrate or prove anything. If they assert a thing, they say that ought to be enough, and they decline to go further. Now, this is both wrong and weak. Only here you must not misunderstand We do not say that assertion is never enough to warrant belief. Sometimes it ought us. to be enough, and sometimes it ought not. Let us show this more fully. Were your teacher to tell you that he had consulted your parents, and that they agreed in wishing you to go through a course of practical geometry, it would be worse than rude for you to ask for proof of the assertion. Your teacher's means of knowing your parents' wishes and his general veracity are quite enough to warrant your acceptance of his statement. But if you were told that your belief in the Bible is all a mistake, and that Mormonism is the true faith, you would not be justified in taking this statement without proof. In the first place, allowing his sincerity, you might fairly inquire whether your informant really knew enough of both to judge between them. And in the second place, you might say, that, as the question is one that you can inquire into for yourself, and is of the utmost personal importance, you must at least have proof before you give up a valued possession. Hence, we say, some subjects are beyond the reach of demonstration, such as the assertions of travellers, and must be received or rejected on the veracity of the narrator. Some can only be investigated by means of knowledge beyond our reach. Here again the decision must either be held in suspense, waiting the fuller knowledge requisite, or must be accepted on the strength of the competence and integrity of those who advance it. Other subjects are open to proof, and, as a rule, we do well to demand and examine such proof. Without saying that we include all sorts, we will, for convenience, say that we have proofs of three distinct kinds,-mathematical, scientific, and moral or religious. As regards the first,-mathematical demonstration. We believe the truth of the multiplication table. You give me the following sum to work-714 × 7, and I bring in 4,993 as the result. You have no hesitation in saying that you can prove my result to be wrong. You appeal at once to the admitted authority, the table, and I am forced to yield. All mathematical principles may be dealt with somewhat in this way. In science we meet with facts and theoriesThe first can generally be tested by actual observation. Thus, a chemist tells us that a lighted taper burns far more brilliantly in oxygen gas than it does in common air. We can very easily try the experiment, and so confirm or deny the statement. Scientific theories cannot be so easily disposed of. As, however, we have given several illustrations of how these may be dealt with, we will only say here, that a theory is considered to have been proved when it meets all the known facts, and these are sufficiently numerous to warrant a general conclusion. In matters of morals and religion, we appeal first to reason and conscience; and, as a final authority, to the Bible, as containing the re vealed will of the ALL WISE and the ALL GOOD. Home Exercise.-1. Define adopted, belief, statement, demonstration, and narrator. 2. Give instances of what may be accepted without proof, and with proof. 3. Give a mathematical proof. 4. Prove on Bible authority that selfishness is a sin. THE VOICES AT THE THRONE. Sabbath, the rest day. Melody, a succession of Rapture, a high state of Hallelujah, praise ye Stole, came in quietly. Blended, united with, so Reverberate, to sound back again. Abysmal, without bottom. A LITTLE child, A little meek-faced, quiet, village child The oft-repeated burthen of her hymn, A seraph by the throne In the full glory stood. With eager hand He smote the golden harpstrings, till a flood |