Fig. 17, a Hindoo Picotah. where the stream that "River." 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, comes down from the glen enters our well. 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, For often, at noon, when returned from the field, 21. Then soon, with the emblem of truth overflowing, As fancy reverts to my father's plantation, And sighs for the bucket which hangs in the well; The moss-covered 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 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 the same axis. an undershot wheel, placed in the current. The force of the current turns the wheel, which moves the machinery connected with it. 23. John. There is an old wheel of this kind at the foot of the cascade which we are just coming to, and that will give us a practical illustration. George. Where the streams are small, rapid, and have sufficient fall, I have frequently seen mills driven by what is called an overshot wheel. The water falls upon the wheel, and by its weight, principally, turns it. Frank. There is also a water-wheel, called the breast-wheel, which receives the water against the side of it instead of the top or the bottom. In this case the water acts partly by its momentum and partly by its weight. 24. Mr. M. Of these wheels the overshot is the most powerful; but both that and the breast-wheel require a considerable fall of water, while the undershot wheel, which is the least powerful, requires merely a strong current. Ida. I have seen the experiments with what is called "Barker's mill," which is moved by the pressure of a column of water.* 25. Ella. Here is the cascade itself; and there, at the foot of it, is the old wheel which John spoke of! I understand now what an undershot wheel is. Ida. And don't you see-where the water tumbles over that ledge another little wheel? That is a breast-wheel. How swiftly it spins round! Ella. And there is still another and larger wheel lower down! That is an overshot wheel. It does seem as though some one has had all these wheels put up for the purpose of illustrating this lesson in hydraulics! *Fig. 20, Barker's mill. In what is called "Barker's mill," the machinery is moved by hydrostatic pressure. It consists of a hollow clyindrical pipe, A B, of considerable height, terminating above in a funnel-shaped cavity, resting below on a pointed steel pivot, and communicating below with a cross tube, or arms, E F, closed at the extremities, but having openings on the opposite sides, near each end of the cross tube. A pipe, G, above, regulates the supply of water, and keeps the vertical pipe full. If the openings at E and F be closed, it is evident that the hydrostatic pressure in the cross tube will be the same on all parts of its surface, and will be proportioned to the height of the pipe A B; but let the water flow at the orifices, and there will be more pressure on one side of the cross tube than on the other, and the machine will revolve in the direction of the greater pressure. The movement of Barker's mill was long attributed, but erroneously, to the reaction of the jets (pressing upon the elastic air) against the extremities of the cross tubes. On the principle of hydrostatic pressure, as here illustrated, the turbine wheel has lately been invented. It is the most powerful and economical of all water-engines. See Fig. 21, next page. 26. All seemed to be of the same opinion; while Mr. Maynard only smiled, and said he hoped they would examine all the wheels, and be able to give a full description of them at another time. All were soon busy in clambering up the rocks, and noticing the working of the wheels; and after some time spent in this way, all returned to the foot of the cascade, when John described the new turbine wheel which his father had lately had put up in his mill, and which is moved by the action of the pressure of a column of water.* "This wheel," said Mr. Maynard, " can be made to utilize from three fourths to four fifths of the theoretical power of the water, while the undershot wheel will not often give to machinery more than one quarter of the water power. The breast-wheel, when well constructed, will utilize a little more than one half of the moving power of the water, and the overshot wheel about two thirds." Before the little party left this pleasant spot, Frank happened to remark that the numerous little water-falls in this cascade forcibly reminded him of Southey's poem about the "Cataract of Lodore,' ""for the water," said he, "comes running, and jumping, and dancing, and leaping down in almost every imaginable variety of form and motion." Thereupon. Frank, being invited to recite the poem, gave the following: THE CASCADES OF ROCKY GLEN. [The Cataract of Lodore.] "How does the water come down at Lodore?" Anon at the word, There first came one daughter, *Fig. 21, the turbine wheel, consists of a fixed P To second and third the request of their brother, And to hear how the water comes down at Lodore, With its rush and its roar, As many a time So I told them in rhyme, For of rhymes I had store. From its sources, which well In the mountains;. Its rills and its gills; Through moss and through brake, And through the wood-shelter, Hurry-skurry. Here it comes sparkling, Swelling and sweeping, Flying and flinging, Eddying and whisking, Turning and twisting, |