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timate of the total resistance of a surface three hundred feet long, such as the side of a ship, whether we assume such increase to continue at the same rate throughout the last two hundred and fifty feet of the surface, or to cease entirely after fifty feet.—Proc. Brit. School of Adv. Sci., 1874.
THE MOVEMENTS OF WAVES AND VESSELS AT SEA.
The study of the motions of vessels is prosecuted in the French navy with considerable diligence by means of the apparatus invented by Madamet, and described in a note in the Maritime and Colonial Review, May, 1876. This apparatus consists essentially of a Foucault regulator causing two pencils to traverse a cylinder with perfect regularity; the whole apparatus being swung on gimbals in such a way that every movement of the vessel is registered, as regards direction, velocity, and time, on a sheet of paper. This apparatus has been used on board of a number of French frigates, such as L'Océan, La Minerve, and La Galissonniere, while lying in the port of Brest, in order to determine completely the movements of vessels oscillating in a calm sea. At present the apparatus is employed in connection with that devised by Risbee, in order to measure the resistance of a vessel to careening.- Revue Maritime et Coloniale, May, 1876, 481.
VIBRATION OF FLUID COLUMNS. The fact that a column of air can be set into longitudinal vibration has suggested to Kundt the possibility of producing similar longitudinal vibrations in columns of water. To this end he sets the tube containing the water in vibration, and finds that the success of his experiment depends principally upon removing from the liquid all traces of gas, whether the latter be absorbed or are in the shape of minute bubbles. The gases absorbed by the liquid are partially driven out by the vibrations, and appear as disturbing bubbles. The so-called tone figures of Kundt can be shown in the vibrating columns of liquid as well as in those of air, and can be used to determine the velocity of sound in the liquid. It is found that the thickness of the glass tube has an influence on the velocity of sound, such that the thicker the tube the more rapid is the propagation of the sound wave.-19 C, VIII., 7.
ON THE THEORY OF THE FLOW OF WATER OR GAS. The important work of Boussines, entitled “ An Essay on the Theory of Currents of Water," which will be printed by the Academy of Sciences of Paris in the twenty-third volume of its foreign memoirs, has received some interesting additions from its author, among which is one that treats on the transpiration of gases, which interesting subject is known to us at present only through the observations of Grohan, Exner, and others, but whose results are explained by the mechanical theories of Boussinesq. Other additions are those that relate to the uniform regimen of flowing water, and especially, the third addition, that which serves to complete the theory of vertical waves, in which the author cal. culates the loss of dynamic energy that the waves experience as a consequence of the mutual friction of the layers of liquid as well as the friction against the containing walls. -6 B, LXXXI., 466.
HYDRAULIC INVESTIGATIONS IN INDIA. A very extensive series of experiments by Captain Allen Cunningham on the flow of water in rivers and canals is published as an extra to the professional papers on Indian engineering. After noticing the results derived from Humphrey and Abbott's study of the Mississippi, D'Arcey and Bazeir's studies in France, and Redy's studies on the Paraguay, Uruguay, and La Plata, he states that the primary object in his own investigations has been to test the applicability of the results of the American and French experiments to large bodies of water in regular channels.
Among the conclusions to which his own observations have led him are the unsteadiness in the motion of a large body of water, even in a uniform channel of great length; the velocity at any point varying considerably from one instant to the next, althongh the average velocity is sensibly constant. The curve representing the surface velocity of a current of water is strikingly regular, and is symmetrical with reference to the mid-channel, while its form depends upon the figure of the cross-section. In a very wide channel it has a flat curve. In a rectangular section in masonry it is approximately a quartic ellipse. The surface velocity near the mar
gin decreases very rapidly, and at the margin itself is perhaps at zero. In cases of straight margins of great length there is a constant surface motion from the margin toward the centre, most intense at the margin. The average central surface velocity varies on a calm day nearly as the square root of the central depth. The curve representing the mid-channel vertical velocity is approximately a common parabola, whose axis is usually below the surface at a depth depending upon the state of the wind; but the form of the curve is hardly well enough determined to admit of inferring the bottom velocity. The line of maximum velocity is highest at mid-channel, and deeper as we proceed toward the margins.- Professional Papers on Indian Engineering, October, 1875.
GAUSS' THEORY OF CAPILLARITY. Plateau states that, as is well known, Gauss has deduced formnlæ relative to particular phenomena of capillarity, by starting from the principle of virtual velocities. The French scientist Moutier has recently shown that the theory of Gauss properly treated explains certain effects attributed of late years to the tension of liquid surfaces, without any necessity of especially assuming the existence of such tension. He has deduced also a general formula concerning the equilibrium of two liquids contact with each other and with a solid. This formula contains certain constants relative to the different molecular attractions that obtain in the system; and now Van der Mensbrugghe, of Ghent, demonstrates that these constants themselves have a definite physical signification; that they represent, viz., respectively the tension at the free surface of the two liquids, the tension at their common surface, and the tensions at the surfaces of contact between the liquids and the solids.-Bulletin Acad. Royale des Sciences de Belgique, 1875, 366.
LIPPMANN'S EXPERIMENTS ON CAPILLARY ATTRACTION AND
HIS ELECTRO-CAPILLARY MOTOR. The facts in relation to capillary attraction, described by Mr. Lippmann, and of which he has availed bimself in the contrivance of what he calls the electro-capillary motor, now exciting so much attention in Europe, are not original with him, but are due to Dr. Draper, who discovered them
more than forty years ago, and made them the subject of a memoir inserted in The Journal of the Franklin Institute of Philadelphia, January, 1836, and again in The London and Edinburgh Philosophical Magazine, March, 1845, in a paper entitled “Is Capillary Attraction an Electrical Phenomenon ?” In these memoirs Mr. Lippmann's facts are set forth, and the explanation of them is given. Dr. Draper formerly wrote a good deal on capillary attraction, regarding it simply as an electric phenomenon. His views on the subject are given in detail in the scientific journals above named, and also in the American Journal of Medical Sci
ON THE ELASTICITY OF GASES. One of the most extensive experimental researches of modern times is that now being prosecuted by Mendelejeff on the elasticity of gases, the expenses of which are being defrayed by the Imperial Russian Society of Technology, the first of which is now published in the Russian language. Experiments made by Oersted, Rumford, Natterer, and Cail. letet lead one to think that under considerable pressures
all gases are compressed less than they should be as indicated by Mariotte's law. The greater part of the first volume of Mendelejeff's work is of course occupied with preliminary researches necessary to establish the accuracy of his instruments and methods. The volume concludes with a description of the first experiments made by him upon rarefied gases and
upon air compressed under from one to three atmospheres. The results that he has obtained in operating upon air, hydrogen, and carbonic acid, under gradually decreasing pressures, lead to the conclusion that the product of the pressure into the volume diminishes with the pressure; the diminution being especially sensible for air, when the pressure becomes very feeble.-6 B, LXXXI., 501.
THE ELASTICITY OF PURIFIED AIR. Some researches of Mendelejeff and Kirpitschoff show that the product of any volume of air by its pressure, which according to the law of Mariotte should be constant for all pressures, is not so for the air, varying considerably when the pressures diminish to so small a quantity as balf a millimeter. This product in fact, which for perfect gases is constant, varied rapidly in the case of air. The deviations from the law of Mariotte for rarefied air are contrary to those observed by Regnault for compressed air. In fact, the product increases when the pressure increases, and diminishes when the pressure diminishes. These discordances are far larger than the possible errors of observation.
AIR PUSHED IN FRONT OF A PROJECTILE.
In investigating the various phenomena attending the impact of projectiles, Busch has studied the question as to whether a sphere falling into a fluid drives air before it, or whether the air is simply inclosed by the water as it comes together behind the sphere. The simple apparatus employed by him to study the question consists of a cyliudrical vessel full of water in which a plate is hung having in the centre an opening so large that the sphere falling through the water will be caught by it. His experiments show that in the case of bodies falling with a very small living force, the air above the water has time to be completely pushed aside by the falling projectile. But that if the living force of the body is increased slightly to a certain limit, it no longer becomes possible for the air to be entirely pushed aside; but that a certain amount is pushed by the sphere forward, and the quantity of air so driven on increases with the increase in the living force to precisely the degree required by the measurement of Magnus, upon the quantity of air carried with the projectile into the water. If we increase the resistance of the fluid by taking some more viscid fluid than water, such as glycerine or oil, it is found that a greater living force is required in order to carry. the air in front of the projectile into the fluid. Even in the case of a shot penetrating a solid body, such as a thin sheet of India rubber stretched over the opening in the plate, a certain quantity of air is driven through in front of the ball.-Verhandi. Naturhist. Vereins, Bonn, XXXI., 251.
ON THE PROPULSION OF AIR BY A JET OF AIR OR VAPOR.
An interesting and practically valuable series of experiments has been made by Romilly on certain phenomena, which may be described as the dragging or propulsion of