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(10642) H. R. writes: Having had a discussion with an acquaintance bearing on the working principle of a syphon, I wish an authority to settle the dispute, as neither has convinced the other to his view. I maintain that the weight of water in the "draw" lifts the water in the "lift" and that by keeping the weight of water in the "draw" greater than that in the "lift" the flow can be kept up; meaning that the "draw" end of the syphon must be longer than the "lift" end. The other party maintains that the syphon operates through atmospheric pressure. That the air being drawn from the pipe and replaced by water, the atmosphere by its pressure on the body of water to be moved forces the water through the syphon. At the end where the water flows out of the pipe he claims the atmospheric pressure has been removed. He won't see that the pressure is the same at both ends. I also maintain that water will lift or pull water, as it does in the syphon, claiming that when the pipe is filled and no air allowed to leak in, the molecules of water are held together by the equal pressures of air at both ends of the syphon, thus preventing segregation. He maintains that water cannot lift or pull water, because it is a liquid and not cohesive. The discussion arose by the intention of a coal mining company of which I am a director to syphon the water from air workings. The water will have to be lifted a vertical height of about 175 feet. A plumbing contractor here whom we consulted in regard to pipe told us we could not syphon water where the lift was more than 60 feet vertical at sea level, and at this altitude (4,500 feet) not more than 40 feet. We have already easily syphoned water over a vertical height of 60 feet, so we knew he was wrong. I would like to know also o an instance of the greatest height over which water has been [ syphoned, if you know one. A. A syphon operates by the pressure of the atmosphere. This fact is fully demonstrated in text books of physics. The pressure of the atmosphere Is I equal to that of a column of water 34 feet at ' sea level, so that no syphon can lift water ! any higher- than that. Indeed 28 to 30 feet is as high as it is practicable to carry water by a syphon. Experiment has fully confirmed the theoretical deductions. It is true that the greater weight of water in the outflow pipe determines the direction of the stream, but the water is lifted into the other arm of the syphon by the pressure of air on the water in I the reservoir. When this arm is longer than 34 feet the pressure of the air is not able to lift the water to the top of that arm and water cannot run over the bend of the pipe. Except for the presence of water vapor a vacuum exists in such a pipe above the water. Because of the air always present in running water a syphon will not carry water to its full theoretical height, and in many syphons it is necessary to provide an outlet for this air at the top of the pipe. You will find the syphon discussed in books of civil engineering such as Trautwine's, price $5.00. Your friend is quite correct in his statement that water cannot draw water along in a pipe, since water is almost destitute of cohesion. The altitude of your place will reduce the height of the syphon about 6 feet, so that you can raise the water only 22 to 24 feet, according to the height of the barometer at the time. You cannot raise water by a syphon any higher than it may be raised by an ordinary lifting or suction pump at the same time and place, Any claim to have raised water 60 feet by a simple syphon is certainly an error. (10643) C. E. B. writes: 1. In your answers to Query No. 10489, C. E. B., I think you have slightly misunderstood question 2. I did not mean the magnet to carry the armature as a hook would, but to lift or attract it to itself. The argument I wished the questions to settle was this : A says that if the armature of a permanent magnet is taken off by sliding it from the poles to the neutral part it will need less total energy to remove it than the magnet expended in drawing it up Therefore, if the magnet in the question would even in theory, go on lifting the armature forever, it would give out more work than was ever put into it, and that is impossible. B thinks that the magnet merely acts as a spring. When the armature is drawn off, it is like stretching the spring, and when released it springs back into place. He cannot, however, give any clear theory to explain the 'stretching." They would like you to decide which is nearer the mark. A. The modern conception of a magnet is that of elastic and self-repellent lines of force passing out of the positive pole and returning through the magnet by way of the negative pole to their starting point. When an armature comes near the magnet, these lines of force enter the armature because iron presents less resistance to their passage than does any other known material, and because of the elasticity of lines of force the iron is pulled to the magnet. When the armature is pulled off, the lines of force are stretched until they break. The pull necessary to break them is obviously equal to their pull in the opposite direction when they pulled the armature toward the magnet. We do not see that the direction of the pull makes any difference. Sliding the armature along the magnet only changes the direction of pull and not its quantity. The same lines of force are ruptured in each case. No adhesion exists between the magnet and its armature. We are unable to think that there is any less force required to remove the armature than the magnet has exerted in drawing it to itself, since all the force there is in either case is due to the magnetic lines which the iron of the armature is capable of containing at the degree of magnetization which the magnet possesses. We do not think A is right in his position. B has an indefinite idea that something stretches, and that is correct. Lines of magnetic force stretch and this requires work. When the lines of force give way, the magnet returns to its original condition. B is more nearly correct than A is. 2. There seems to be great difficulty in making telescope object glasses over about 40 inches. Would it be possible to arrange a number of small glasses, say six 30-inch, in a circle, all focused, by means of prisms, on a common eyepiece and so adjusted that all the images coincide? A. It would seem impossible to adjust images from several lenses so as to produce a well-defined image in an eyepiece common to all the lenses. It is difficult to do so with even two or three lenses in projecting upon a screen in the three-color process of projecting pictures in natural colors. It would be much more difficult if an accurate magnification of the combined images were to be made.
This article was originally published with the title "Notes and Queries"