Silliman's " Principles of Physics " contains, on page 336, section 386, the following description and explanation of intermittent springs: ; " There exisit in natureialerrai'ttentseringa,tnewatei flow, ing regularly for a time, and then suddenly ceasing. In these Springs, the opening, as at A, in Fig. 1, communicates with a cavity, C, by means of a channel, A B D, which has the form of a syphon. This cavity is gradually filled, until, at last, the water attains the level, B B, when the syphon is filled and the water escapes. If the syphon discharges the water faster than it flows into C, after a time its level would be lowered to D; air would then rush in by the syphon, the flow of water would cease, and would not recommence until it had again attained the level, B B." This theory of intermittent springs is substantially the same as that given by all textbooks on physics, and it is either an insufficient or an absurd one, as we shall proceed to demonstrate. We shall find it necessary, however, to first discuss the operation of the syphon. A syphon is a bent tube, having one of its legs longer than the other. (See Fig. 3). When the syphon is filled to any point, I, below the fluid,J, in which the shorter leg is immersed, the fluid will commence to flow until the level of the fluid, in the containing vessel, reaches the bottom of the shorter leg, when the flow will suddenly cease. The cause of the Jfae of the fluid in the shorter leg is atmospheric pressure, the pressure being removed from the section, G H, by the depending weight in the longer leg. If, when the fluid in the containing vessel-becomes exhausted, it be JSpte" with mffheient rapiditytill its level rises above the bend in the syphon, the syphon will again commence to flow, and will exhaust the fluid in the vessel, if its discharge is greater than the supply after the flow commences. Operated in this way, with a greater supply than the capacity of the syphon before the flow commences, and a less supply afterward, until the dischargefrom the sypton Should cease, it would be an intermittent founr tain, without regard to the size of the bore of the tube, which we will next proceed to consider. The principle of the rise of the fluid in the shorter leg being the same as that of the ortji nary atmospheric pump, the column, as it proceeds over the lower part of the bend, H, must remain solid and unbroken, or the tube will not act as a syphon at all. It will not remain un broken unless the tube be so small that capillary attraction preserves its integrity, or the supply be as great as or greater than the capacity of the tube for discharge, until the end of the column in the longer leg has passed below the level, J, in the cistern; two limiting circumstances, which, if they exist in intermittent springs, have not been noticed in the works on physics, so far as we have been able to discover. We have then to suppose, in. order to substan -tiate the syphon theory of intermittent springs, a remittent supply, trickling into the chamber, C, Fig. 1, greater before the beginning ot the discharge, and less afterward, or to suppose the channel, A B D, a capillary tube. The latter hypothesis is opposed to facts—how about the former? An entirely intermittent supply does not necessitate the hypothesis of a syphon, as that would make an intermittent spring as well through a Btraight channel as a syphon. A constant supply less than the capacity of the syphon, will raise the level in C to the lower part of the bend, B, Fig. 3, when it will commence to flow over, and continue to do so, thus forming a perpetual spring. A constant supply, as great as the capacity of the syphon, will also give us a perpetual spring. We can then account for intermittent springs only by suppos ing an intermittent supply, with any form of channel, or a remittent supply, in connection with a syphon channel. In order that the syphon may w.ork, we must also suppose the air to have free access to the chamber, C, which it may have through cracks and fissures, and not to have such access to the channel—a supposable case, although not a probable one. We believe the theory of an intermittent supply the only one that accounts for the facts. What is the cause of such intermission may form the subject of a future article.The Chicago Equatorial Telescope Prof. Barnard, of Columbia College, has written an interesting letter to the College Courant, of Yale, descriptive of the great equatorial telescope of the Dearborn University of Chicago, of which the Professor says that, if it is not the largest in actual existence, he would not know where to look for a larger one mounted and in use. In comparison with the Harvard equatorial, the Chicago instrument has a light as three to two. The clear illuminating aperture has a diameter of eighteen and a half inches, while that of Harvard measured fifteen. The whole diameter of the Chicago objective, mounting included, is twenty inches. The defining power of this glass is unrivaled, as has been satisfactorily proved by the discovery, it enabled its constructor, Mr. Clark, to make of the companion of Sirius, a star which Was confidently believed to exist, but which had eluded ftie refractors of Cambridge and Pultova (of exactly the same capacity), and the reflectors of Mr. Lessell and Lord Rosse. The history of this magnificent telescope is singular. It was made to order for the University of Mississippi, and was to have been erected in an ebservatory already built and still standing at Oxford, in that State, the order for its construe-194tion having been obtained chiefly through the untiring efforts of Professor Barnard himself. The war :came to change the destiny of the instrument, and Professor Barnard thinks that Chicago would not have been in possession of this magnificent object glass but for the order given by the Mississippi University. It is j ust matter of pride that American skill and science have produced this marvel among telescopes.
This article was originally published with the title "Intermittent Springs—Error in the Works on Physics" in Scientific American 20, 13, 193-194 (March 1869)