Archimedes and Franklin, is indeed a history of one of the most important events in the records of science. In that same lecture is a very interesting account of the visit of the Roman orator Cicero to the grave of the philosopher." 1 JA'-SON, the hero of the famous Argonautic Expedition, as fabled in Grecian history, sailed in the ship Argo to Colchis, in Asia Minor, for the purpose of recovering a "golden fleece" deposited there. 1. 2. 3. LESSON V.—HYDRAULICS-THE EXCURSION. SONG OF THE BROOK. I COME from haunts of coot1 and hern ;2 I make a sudden sally, And sparkle out among the fern, By thirty hills I hurry down, I chatter over stony ways In little sharps and trebles, I babble on the pebbles. And out again I curve and flow, To join the brimming river; For men may come, and men may go, But I go on forever.-TENNYSON. 5. "The day is so pleasant, and the subject of our lesson so inviting," said Mr. Maynard, "I propose a walk by "The River,' where we can better witness some experiments appropriate to our studies. You know that, in plain English, the lesson to-day is about water in motion." 6. "I shall be delighted," said Ida, as they were crossing the lawn, "to study this lesson in the pleasant valley; for I had feared it would be all about mills and resistances of fluids-important enough for millwrights and engineers, but of little interest to Ella and myself. Now I shall ramble where 'Joy smiles in the fountain, health flows in the rills, And the ribbons of silver unwind from the hills.'" 7. Ella. I really fear that Ida and I will learn but little philosophy in this lovely valley, "where streamlets flow and wild flowers blow." Ida, let us study the poetry of the sub ject first. "How beautiful the water is! To me 'tis wondrous fair— No spot can ever lonely be If water sparkle there; It hath a thousand tongues of mirth, Of grandeur, or delight, And every heart is gladder made Where water greets the sight." 8. Mr. M. I am glad you will all enjoy this topic, and that the girls can talk about "ribbons of silver," while the boys are discussing the merits of undershot and overshot wheels; but I shall be disappointed if you do not find that the very poetry of" water in motion" is full of philosophy, and that the philosophy is very poetical. You can all moralize on the subject, also, as you see "The rivers, how they run Like human life, to endless sleep." I think we will continue along "The River" as far as Rocky Glen, where is a fine well of water, with an old-fashioned sweep; and then, if the girls are not too much fatigued, we will follow the glen, and go up to the Cascades, where, as George will recollect, are the remains of an old mill. 9. George. I have been there frequently, and a wild but beautiful spot it is, too. Ida. I have heard so much about the Cascades, I know I shall be delighted to see them. I am sure Ella and I can easily walk as far as that and back again. Mr. M. As we shall have this running stream constantly "babbling" to us, with its "thousand tongues of mirth," as Ella said, let me ask how it is that it has this speaking power'? John. By its motion, I suppose. 10. Mr. M. Then tell me, if you please, what makes the water move at all? John. The bed of the river is an inclined plane, and the particles of water roll down by the force of gravity, just as a marble from a desk. Mr. M. Very well; this force of gravity is such that, in large rivers, a fall of three inches in a mile is said to give a velocity of three miles an hour. George. Would it not be the same in small streams? 11. Mr. M. By no means. The friction of the water against the banks and bottom tends to retard the motion. In pipes the friction is so great that, in a tube one inch in diameter and two hundred feet long, only one fourth as much water will be discharged as would escape from a simple aperture of the same size. Frank. I see the river is much wider in some places than in others. Is not the current the most rapid in the narrowest parts? 12. Mr. M. It is. I have here an instrument called a streammeasurer. It consists of a vertical tube with a trumpet shaped extremity, bent at a right angle. When plunged in motionless water the level in the tube corresponds with that outside, but the impulse of a stream causes the water to rise in the tube until its vertical pressure counterpoises the force. Let us try it first in the wide, and then in the narrow places. You see quite a difference in the velocity. 13. George. I have just thrown some pieces of bark, one near the middle, and the other near the shore. See how much faster the piece near the middle goes down stream. Ida. Before I came to Glenwild I lived in sight of a navigable river, and I used to wonder why Figure 15, the the boats, in descending, kept near the middle, and Stream-mea- those ascending went nearer the shore. I understand it now. Boats going down had more assistance from the current, and those coming up had less resist surer. ance. 14. Mr. M. There is also a greater velocity at the surface than near the bottom from the same cause. John. I think I see why wide rivers are higher in the middle than near the banks. The water, running more swiftly, tends to draw along that on each side of it, which it can not do without lowering the surface on each side. ing water. 15. Mr. M. You must not confound the velocity at the surface of a river, and at different depths, with that of water running from apertures in a reservoir. If in this vessel, Fig. 16, orifices be made at different depths, the velocities of discharge will be as the square roots of the depths. That is, if D is one foot below the surface, and A four feet, a quart will run from A, while only a pint will be discharged from an orifice of the same size at D. 16. Frank. As water will run into a Fig. 16, the velocity of spout- submerged empty vessel with the same velocity that it will flow from a full one, I can see why a leak in a ship near the keel is so dangerous. Mr. M. We have been talking about water in motion; let us now talk about hydraulic machinery. First, can each of you describe some method you have seen, or heard of, for raising water from wells? Fig. 17, a Hindoo Picotah. 17. Ida. I have read, in an old book, of a curious method of raising water in Hindostan. It is called by the Hindoos a picotah. Here is a picture of it, which I think sufficiently describes itself, except that another person must stand by the well to empty the bucket. Ella. We often see in the country a contrivance something like this, called a sweep, or a well- -sweep. Ida. Yes; and there is one yonder, just at the foot of the hill, where the stream that comes down from the glen enters our "River." John. And many a draught of the purest water I have taken from the "old oaken bucket" that hangs there. 18. Frank. That old-fashioned sweep always reminds me of the first home that I knew, before I went to the city to reside, and of Woodworth's beautiful little poem, "The Bucket." How many times I have repeated that poem to myself when thinking of my early home. Mr. M. Perhaps Master Frank will entertain us with a recitation of the piece, while Master George helps us to a practical illustration from the "moss-covered bucket" itself. 19. 20. THE BUCKET. How dear to this heart are the scenes of my childhood, The wide-spreading pond, and the mill which stood by it, And e'en the rude bucket which hung in the well! For often, at noon, when returned from the field, 21. Then soon, with the emblem of truth overflowing, And sighs for the bucket which hangs in the well; Mr. M. Both the poem and the illustration are excellent. All of you have doubtless seen both the common windlass and the chain-pump used for drawing water from wells and cisterns. But do you recollect, George, of a very ancient and singular invention for elevating water called the Screw of Archimedes? George. Very well indeed. It is said to have been used by the Egyptians in draining their land from the overflowings of the Nile. It consists of a hollow screw-thread wound round an axis, and is turned by hand or by machinery. The water continually rises through the spire, and is discharged from the top.* 22. Mr. M. These are but a few of the methods which the ingenuity of man has devised for elevating water. I am glad you omitted all the usual kinds of pumps, as they belong to a future lesson. Can you give me, Frank, a description of any kind of water-wheel for propelling machinery? Frank. I have seen a mill driven by a large wheel called *Fig. 19, the screw of Archimedes. To explain the mode of operation of this screw, suppose a small ball to be dropped into the mouth, A; it will roll down the tube until it arrives at the lowest point, B. If the screw be now revolved, the point B will as- M cend, C will come down lower than B, and the ball will consequently roll to C. In one entire revolution it will roll to D, and in a second to F; and in six |