NW by W N.N.W sels the sails receive the Wbys SW by W b -M'S B-MIN S.S.W Fig. 43. toward h, or in the diagonal of a square, provided the sail could be kept so as to receive the wind as shown at f. 20. Vessels are not round, but long; so it requires much more force to push them sideways than forward. By a proper management of the rudder, not shown in the figure, the ship can be made to sail almost against the wind. When sailing as nearly opposite or against the wind as possible, the ship is said to be close hauled, as those marked a and b. 21. Ida. The whole matter seems very plain to me now. Ella. I fear I shall not so easily understand the answer to my question, as it is perhaps beyond the capacity of a little girl; but no question is too hard to ask. Ever since I heard that philosophers had weighed the earth, I have been anxious to know how it was done. 22. Mr. M. To understand the method pursued by those who have weighed the earth will require a fuller explanation than I have given of the action of gravity. Every particle of matter attracts every other particle, as you have learned ; but the attraction is rapidly diminished as the distance increases. It is inversely 10 as the square of the distance that is, at twice the earth's radius11 from its centre gravity is one fourth what it is at the surface. In other words, a pound of matter, as weighed at the surface, would weigh only four ounces 4000 miles above the surface. 23. If a lead ball were to hang from the top of a tower, it would be attracted a little toward the tower as well as a great deal toward the earth. Now if I can find how much the tower attracts the ball, also the weight of the tower and the position of its centre of gravity, as I know the distance of the earth's centre of gravity, I can find the weight of the earth. Do you understand how? Ella. I confess I am as much perplexed as ever. 24. Mr. M. I did not expect you to understand with so slight an explanation, and am glad to hear you frankly admit that you do not. That is the way to learn. If there were two globes of equal weight, as two earths, for instance, and a ball were suspended from some distant point so as to be only under the influence of the two spheres, 12 toward which would it hang? Ella. Toward neither, but half way between them. 25. Mr. M. You will soon see, then, how the earth is weighed. Let us suppose the spheres unequal; you must understand that the ball would hang nearer the heavier sphere, but still between them. If you knew the weight of one sphere, and the distance apart of the centres of both, and how much nearer the ball hung to one than to the other, could you find the weight of the other? 26. Ella. I think I see now how it could be done, and how the earth could be weighed by these principles; for, if we have the weight of one sphere, its distance from the little ball, and the power exerted by it on the ball, we know that the power exerted by the earth must bear a similar proportion to its weight and distance. It does not appear to me half so surprising as it did before that philosophers can weigh the earth; but it seems more and more wonderful that all things are governed by laws so fixed and uniform. 27. Mr. M. And the more you study Natural Philosophy, the more plain and simple will its principles seem to you, and the more enlarged will become your views of the works of the Creator. The mind that comprehends the wonderful laws, so sublimely simple and beautiful, that regulate the vast universe of worlds, must ever be deeply impressed with the conviction that there is a great and overruling mind which plan ned them all, and which still keeps them in harmonious action. It is impossible for a true philosopher to doubt the existence of a God. 28. Here Mr. Maynard informed the class that, as they had now gone over the first great division of subjects embraced in Natural Philosophy, he would bring these conversations to a close; but he hoped to resume them after a few months, when subjects of still greater interest and more variety, in the same important field, would be presented to them. 29. He remarked that they were but just entering upon the study of Nature's laws, and hoped they would not think they had done any thing more than just to make a beginning. "The more you learn," said he, "the more you will find there is to be learned; and if you are at all disposed to vanity, the less vain will you be of your own attainments. Much knowledge will always cause, in a sensible person, a feeling of humility, in view of how little he can hope to know in this world, even after a long life spent in study, compared with what will still be unknown. 30. "This principle is well illustrated," said Mr. Maynard, "in the words spoken by that eminent philosopher and true Christian, Sir Isaac Newton, a short time before his death. 'I do not know,' said he, 'what I may appear to the world; but to myself I seem to have been only like a child playing on the sea-shore, and diverting myself in now and then finding a prettier pebble or shell than ordinary, while the great ocean of truth lay all unexplored before me.' If the great Newton, with his powerful intellect, and after devoting a lifetime to the study of Nature's laws (which are none other than the laws of God), could utter such a sentiment, how much more becoming are modesty and humility in us." 1 E-QUI-LIB'-RI-UM, a state of rest produced 8 E-LEC'-TRIC-AL, pertaining to electricity. by the mutual counteraction of two or more forces. 2 DE-DUC-TION, allowance; abatement. 4 GRO-TESQUE'-LY, in a fantastic manner. 7 SO-LU-TION, explanation. 9 TRAC'-TION, the act of drawing, or state of being drawn. 10 IN-VERSE-LY, in an inverted order. A term used when one quantity is greater as another is less, or less as another is greater. PART VI. SKETCHES FROM SACRED HISTORY. "Give me understanding, and I shall keep thy law; yea, I shall observe it with my whole heart."-Psalm cxix., 34. "Blessed is he that readeth, and they that hear the words of this prophecy, and keep those things which are written therein.”—Rev., i., 3. LESSON I. THE CURSE OF CAIN. 1. Ir was after our first parents had been driven forth from the garden of Eden, and while they were still living, that the first great crime that stains the annals1 of our race was committed. Cain and Abel were the two sons of Adam and Eve; and Cain was a tiller of the ground, but Abel was a keeper of sheep. 2. In temper and disposition the two brothers were as different as their occupations; for while Abel was meek, humble, and pious, Cain was haughty, envious, and revengeful. When they brought their customary sacrifices before the Lord, the Lord had respect to Abel and to his offering; but unto Cain and his offering the Lord had not respect. 3. Then was Cain angry; and he talked with Abel his brother; and it came to pass, when they were in the field, that Cain rose up against Abel, and slew him. And the Lord said unto Cain, Where is Abel thy brother'? I know not: Am I my brother's keeper'? And he said, 4. And the Lord said', What hast thou done'? The voice of thy brother's blood crieth unto me from the ground. And now art thou cursed from the earth, which hath opened her mouth to receive thy brother's blood from thy hand. When thou tillest the ground, it shall not henceforth yield unto thee her strength. A fugitive and a vagabond shalt thou be in the earth. 5. Thus was Cain cursed, and driven away from his friends and kindred. And he "went out from the presence of the Lord, and dwelt in the land of Nod, on the east of Eden." The CURSE OF CAIN has been thus described: 6. O, the wrath of the Lord is a terrible thing! 7. Like the tempest that withers the blossoms of spring, And, lo! like a deer in the fright of the chase, |