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come acquainted with the simple mechanical powers, and learned their names. What have you to remark thereon ?
Ch. I perceive, plainly, that they are calculated to perform what the strength of any animal could not effect without them; but I must confess I have not understood much of the principles on which they act; besides, nothing has been said in respect of the motion of weight. Fa. What have you gathered from the authors you
have read on that point.
Ch. I understand that the body which is moved, or hindered from moving, is the weight. That which moves or sustains the weight is called the power. By the action of the weight we are not to understand the motion of its centre of gravity in a horizontal line, nor the circular motion of the parts about the centre of gravity: for, in both these cases the gravitation of the body is no impediment to its motion. The motion of the weight is merely the ascent or descent of its centre of gravity.
But are there not, Papa, distinct centres to be considered in connexion with Mechanics in general ?
Fa. Yes; there are three centres. First, the centre of magnitude of a body, which is a point taken as nearly as possible at an equal distance from all the outward parts. Secondly, the centre of motion of a body, which is any point whereon the body may rest, or about which it may move. Thirdly, the centre of gravity of a body, which is a point whereon all the parts of the body balance each other; so that if this point be made the centre of motion, the body may
be placed and continued at rest in any situation. Ch. Can any body stand or retain its position upon
either a horizontal or inclined plane suspended, unless a perpendicular proceeding from the centre of gravity fall within the base ?
Fa. No. In all suspended bodies at rest upon any centre of motion, the centre of gravity is either directly over or directly under the centre of motion.
Joyce's Scientific Dialogues. 1. What do you mean by the momentum of a body?
2. Can you make a small body have a 6. Does every part of the minute-hand momentum equal to a large one?
travel twelve times faster than the hour3. What is meant by one body having a hand? greater velocity than another?
7. What mean you by the centre of mo4. Illustrate this by the motion of the tion of a watch?
5. How much slower does the hour hand travel than the minute-hand?
hands of a watch.
8. What parts of the vanes of a wind- 16. When you stir the fire with a poker, mill move the fastest?
what forms the fulerum? 9. Whether does the boy in the outer 17. By means ot what forces do the heav. seat of the round-abouts or the one in the enly bodies move round their centres ? inner seat get the longest ride?
18. What made the Colonel of the cavalry 10. Naine the six Mechanical powers. regiment smile on lending his regularly.
11. What limits the assistance gained trained horses to the yeomanry? by these powers ?
19. When the bugle suddenly sounded 12. Explain by an example what you a balt, what happened to these gallant mean by the phrase "what we gain in soldiers ? power we lose in time.”
20. What mean you by the centre of 13. Whatis meant by a fulcrum ? magnitude of a body? what, by the centre 14. What is the fulcrum of a watch ? of motion of a body? what, by the centre of
15. Why is the pivot on which scissors gravity ot a body? move, called a fulcrum ?
VI.-THE HAND OF GOD IN HISTORY. The Scriptures are full of illustrations of the truth, that God overrules, for the ad. vancement of Christ's kingdom and glory, all the affairs of men,-and, perhaps, it might be a profitable exercise for you, my dear scholars, to search the Bible at home, for instances of this cheering truth, in the history of the individuals there spoken of, and also of the nations. You will find the bistory of Joseph, recorded in Genesis; of Moses, in Exodus ; of David, in I. Samuel. I will just inform you here, that Law. rence Koster, a man of Haarlem, town in Holland, four centuries ago, (1430) discovered the art of printing, while amusing himself with cutting letters in the bark of a tree, and making impressions of them on paper. Claudius Ptolemy, spuken of in the lesson, was a celebrated astronomer and geographer of Egypt, who lived about 160. B.C. He was the author of that solar system which considered the Earth as the central point of the heavens. His work on Geography was used as a manual for centuries. It cannot but interest the pious mind, and confirm the wavering, doubting soul, and quell the rising fears of unbelief, and give confidence in God's purposes and promises, and foster a delightful anticipation of the certain triumph of Christ's kingdom on earth, to see how, out of small beginnings, God is wont often to bring the most stupendous results ; setting at naught the wisdom of man; ordering strength out of weakness, and making the most wonderful effects follow the most unlikely and insignificant causes. The following instances will further illustrate the mode of providential agency in carrying out the great work of human salvation :
It was a small matter that Joseph should dream a dream; or that the daughter of Pharaoh should discover, while bathing in the Nile, an ark of rushes, floating on the river ; or that the same casualty should befall Daniel which fell to the lot of many a noble youth of that day, to be transported from his native hills of Palestine to an unwelcome captivity in Babylon. Each of these seemingly unimportant incidents was the first link in a chain of stupendous events. Great and noble purposes were answered by the captivity of Joseph in Egypt, and of Daniel in Babylon; and, perhaps, to no mere man that ever lived, has the Church and the world been so much indebted as to Moses. He was a signal instrument in the hands of God for civil, social, and moral advancement. In that little rush-bark lay the germ of the most extraordinary reform and advancement in every thing that pertains to the best interests of man, both in this world and the world to come.
Or we might speak of David : the trivial circumstance of his being sent, when a mere lad, with supplies for his brethren, who were serving in Saul's army, leads, very unexpectedly, to his successful encounter with the giant; to his signalizing himself in the sight of all Israel, and to the illustrious course which he afterwards pursued as the head of the chosen nation, and the guide and teacher of the church. He was an illustrious type of Christ, and an extraordinary instrument in forwarding the great work of human salvation. No one can trace up, step by step, the history of the son of Jesse, from the time that, in obscurity and in his childish simplicity, he watched his father's flocks in Bethlehem, till with a “perfect heart," he sat on the throne of Israel, and wielded the destinies of the chosen tribes, and not admire the wonderworking hand of God, in so controlling human events as to bring the most extraordinary and far-reaching results out of the most simple, and, apparently, insignificant causes.
Profane history furnishes illustrations scarcely less interesting, of the same overruling Hand, so controlling all the events of this lower world, as best to subserve the great scheme of redemption.
A little mistake, (probably a mishap of ignorance,) is made by Ptolemy in drawing up a map of the world. He extended the eastern part of the continent of Asia so enormously as to bring it round almost in contact with the western parts of Europe and Africa, of course making the distance across the Atlantic ocean to Asia but trifling. Consulting this map, Columbus conceived the idea of effecting a passage to India by a westerly route. Hence the discovery of America. And though he must first discover Ptolemy's mistake, and encounter difficulties of which in the outset he had no conception, yet his mind having become fired with ardour for discovery, his preparations being made, and his zeal not easily abated, he pressed forward, not over a sea of a few hundred miles, but of thousands, till the expected land appeared. “A little fire" was kindled in his ardent soul for discovery, the result was an immensely “great matter,” the discovery of a new world, the magnitude of which we have yet scarcely more than begun to see, and which we can never estimate, till we shall see the end of the magnificent plans which God has to accomplish in connection with the American continent.
So it was a little matter that a Dutchman should cut a few letters of the alphabet on the bark of a tree, and then, by means of ink, transfer an impression of them on paper. But here was the rude idea of printing. Nor did it seem a much greater matter that he should, (as the first improvement of the art,) cut letters in blocks of wood, which he used for types, to print whole pages for the amusement of his children. This was the day of “small things.' But if you have a mind far-reaching enough to measure the present power of the press, its power to perpetuate the arts and sciences, to control mind, to instruct and reform men, and by a thousand ways contribute to the advancement of our race, you can tell how great a matter” this art of printing is.
Again, an obscure Highland boy is taught the first principles of our religion by his humble parents amidst the glens of Scotland. He early learns to revere the Bible, and to honour God and the religion of his fathers. We next hear of him, in mature years, a marine on board a British man-of-war. A battle rages. The deck is swept by a tremendous broadside from the enemy. Captain Haldane orders another company to be “piped up” from below to take the place of the dead. On coming up they are seized with a sudden and irresistible panic at the mangled remains of their companions strewed on the deck. On seeing this, the captain swore a horrid oath, wishing them all in hell. A pious old marine, (our Highland boy,) stepped up to him, and, very respectfully touching his hat, said, “Captain, I believe God hears prayer, and if he had heard your prayer just now, what would have become of us?” Having spoken this, he made a respectful bow, and retired to his place. After the engagement, the captain calmly reflected on the words of the old marine, which so affected him that he devoted his attention to the claims of religion, and became a pious man.
Through his instrumentality his brother, Robert Haldane, though at first contemptuously rejecting his kind attentions, was brought to reflection, and became a decided Christian.
James Haldane, (the captain,) became a preacher, and is
pastor of a church in Edinburgh. Robert subsequently settled in Geneva ; and being much affected by the low spiritual condition of the Protestant church there, and the theological views of the clergy, he sought an acquaintance with the students of the theological school, invited them to his house, gained their confidence, and finally became the means of the conversion of ten or twelve, among whom were Felix Neff, Henry Pyt, and J. H. Merle D'Aubigne. Few men have so honourably and successfully served their Divine Master as Neff and Pyt; and few fill so large a sphere in the world of usefulness as the President of the theological school at Geneva, and the author of the immortal History of the Reformation ; and few spots on earth are so precious to the truth, as the city of Geneva. It was a “ little fire” that kindled these great lights, and made the ancient and honourable city of Calvin once more worthy of that great name; it was a little spark, struck from the luminous soul of a poor Highlander, and well lodged in the soul of his unpretending boy.
After preaching successively and successfully in Berlin, Hamburg, and Brussels, D'Aubigne was, providentially, brought back to Geneva, his native city, which event led to the establishment there of the present evangelical “school of the prophets," with D’Aubigne at its head. This seminary is the hope of piety in Germany; the citadel of the doctrine of the ever blessed Reformation ; a fountain sending out the healing streams of salvation to all Europe, and to the waste places of the Gentiles.
There is brought to our recollection the case of a yet larger river which arose from a still smaller rill: A Welsh clergyman asks a little girl for the text of his last sermon. The child gave no answer ; she only wept. He ascertained that she had no Bible in which to look for the text. And this led him to inquire whether her parents or neighbours had a Bible : and this led to that meeting in London in 1804, of a few devoted Christians, to devise means to supply the роог in Wales with the Bible ; the grand issue of which was the formation of the British and Foreign Bible Society, a society which has already distributed more than 15,000,000 copies of the Bible ; its issues now reaching nearly a million and a half annually. And this, in turn, led to the formation of the American Bible Society, and to the whole beautiful cluster of sister institutions throughout the world, which are so many