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the atmosphere along with a jet of air or vapor. Any such jet, blown from a fine spout, carries with it a certain quantity of the surrounding air. From an extensive series of accurate measurements made by him, he concludes in general that when the jet is received through a tube into a chamber pierced opposite to the receiving spout by an orifice equal and similar to it, the pressure within the chamber is reduced to one half. Second, that whatever distance the orifice of the spout may be, the effect is always greater if the direction of the jet is the same as that of the axis. In all directions inclined to the axis the effect diminishes very rapidly. The experiments made by him bave included the use of conical and cylindrical tubes, and open and closed reservoirs.—6 B, LXXX., 189.

EXTENDING THE COMPASS AND INCREASING THE TONE OF

STRINGED INSTRUMENTS. At a recent meeting of the Musical Association of London, Dr. Stone stated that there are three ways in which a string may be made to give very slow vibrations, viz., by increasing its length, its thickness, or its density. He had adopted the third plan by covering a catgut string with heavy copper wire, which proved to be fairly successful. This had been improved upon by re-enforcing the vibrations by means of longitudinal struts or bars, applied to the double bass violin. Four strips of white-wood, curved to an elliptical figure, are passed parallel from end to end, on the inside of the belly of the violin. The result is the removal of what is termed by the musicians “wolf,” or inequality and falseness of tone, with a great increase of power throughout the range of the instrument. The same process is equally applicable to small violins, and the bars can be removed at pleasure without damaging the instrument. As an illustration of what may be effected by this system, an instrument whose original cost was 18. 9d. was exhibited to which this improvement had been applied, and its performances called forth great applause.-18 A, XX., 270.

CONDUCTION OF HEAT BY BUILDING MATERIALS, The coefficient of conduction for heat of various building materials has lately been carefully investigated by Lang,

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who, in his studies, has endeavored to exclude the influence of radiation, and has made measurements by means of the thermo-electric multiplier. He finds that the stones considered by him are much better conductors of heat when wet than when dry, and that various classes of stones, such as marble, sandstone, granite, etc., have approximately the same co-efficients of conduction, while bricks of all kinds are much worse conductors than the natural stones.

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CHANGE OF TEXTURE IN SANDSTONE BY HEAT. According to Mr. John Young, the sandstone bottoms of iron furnaces assume, from the long-continued action of heat, a distinctly columnar form, the old lines of stratification being obliterated, thus showing that heat, as well as electricity and mechanical force, was an agent in the production of the columnar form of rocks.-15 A, November 20, 676.

Mr. Toduce eers,

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ANTIQUITY OF THE BURNING MIRROR. Buchwalder states, in reference to the burning mirror recently invented by Mouchot, that it was used as long ago as in the days of Numa Pompilius, in whose reign the priests in the temple of Vesta, according to Plutarch, employed a conical reflector, with a solid angle of ninety degrees, as a mirror for concentrating the rays of the sun, thereby producing the heat necessary to light the sacred fires.

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OBSERVATIONS UPON RADIOMETERS. Mr. H. A. Carrington communicates to the Popular Science Revievo a slight contribution in the way of experiments with radiometers, in which he has arrived at the following conclusions: First. That when the radiometer is receiving light or heat, being at a lower temperature than its surroundings, repulsion of the black disks must ensue, and continue until the temperatures are equalized. Second. When the radiometer is radiating heat, being at a higher temperature than its surroundings, attraction of the black disks, or the apparent repulsion of the white disks, must ensue, and continue until the temperatures are again equalized. Third. No source of light can produce repulsion of the black disks unless it is capable of raising the temperature of the residual air within the globe. Popular Science Review, April, 1876, 137.

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OBSERVATIONS ON THE THEORY OF CROOKIES' RADIOMETER.

Professors Dewar and Tait, in the prosecution of their researches into the movements of Crookes' radiometer, have devised methods of producing very perfect exhaustion of air from a receiver; the most perfect vacuum being obtained by taking advantage of the absorbent power of charcoal. The movement of the radiometer, whose disks are of rock-salt, are traced to the unequal heating of the movable parts of the apparatus; and the explanation of the phenomena observed by them is deduced from the kinetic theory of gaseous pressure.- Proceedings Royal Society of Edinburgh, VIII., 628.

THE MECHANICAL PRODUCTION OF COLD, Mr. A. C. Kirk has offered a meinoir on the mechanical production of cold to the Royal Institution of Civil Engineers, which attracted extended discussion, and will probably lead to material improvements in many of the mechanical arts. He states that his attention was first drawn to the subject by noticing the inconvenience experienced at certain paraffin-oil works, where it was customary to extract the solid paraffin in winter by exposing the material to a low temperature sufficient to cause the paraffin to crystallize. At those works chemical methods of producing low temperatures had been introduced in order to avoid the otherwise expensive loss of time. These methods were too objectionable to be continued long, and the author was requested, as engineer to the works, to examine the methods invented by Dr. Gorrie, who had constructed a machine that was said to have produced ice in Florida. Mr. Kirk's early experiments with machines similar to those of Dr. Gorrie having been unsatisfactory, attention was turned to an air-engine, the reversal of whose processes it was thought ought to make a good cooling machine; and, in fact, after many modifications and reconstructions, a degree of cold was produced by it sufficient to freeze mercury.

This machine may be in the main described as follows: A steam-engine moves a piston backward and forward, by which the confined air is in a state of alternate compression and expansion. While the air is compressed in one space, the heat generated thereby is

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removed by a stream of water flowing through properly arranged pipes; and while the air is expanding and cooling in the other space, heat is abstracted from whatever has been placed in a second properly arranged receptacle. The only limit to the temperature attainable is the conducting power of the material of which the apparatus is composed. The air contained in the pistons may be at any pressure that the apparatus can withstand. The machines built for cooling large masses of water for the use of breweries, etc., are usually worked at from 100 to 120 pounds per square inch, the efficiency and capacity of the machine increasing with increased pressure. To keep up this pressure and meet leakage, a small compressing pump draws air through two boxes containing chloride of calcium. This is necessary to dry the air, for if the air be damp the moisture is deposited as snow in certain parts of the apparatus, and causes mischievous obstructions.

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A NEW ICE CALORIMETER. The ice calorimeter in all its forms measures quantities of heat by determining how much ice that heat can melt. In Bunsen's apparatus advantage is taken of the change of volume which ice undergoes upon fusion. This change occurs at one end of a column of mercury sustained in a capillary tube: as the ice melts the mercury descends, and the amount of fall represents the quantity of heat. But the use of a capillary tube in this apparatus affects the delicacy of all measurements made with it. So Schüller and V. Wartha propose a modification of Bunsen's calorimeter, in which graduated scales are done away with, the amount of mercury involved in any measurement made with the instrument being determined by direct weight. As the ice in the apparatus melts and the column of mercury falls additional mercury flows in through a peculiar suction tube, and the weight thus absorbed affords a measure of the heat. The details of the new calorimeter are not very complicated, but need the allthor's diagram for their explanation. The inventors tried to apply their instrument to determining the specific heat of some metallio titanium, and obtained a value apparently too high. Seeking the cause of their error, they found that the supposed metal contained nitrogen, being really a compound of the formula TiN2.-35 C, September, 1875.

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EXPERIMENTS UPON NON-LUMINOUS FLAMES. The experiments by Knapp, and the subsequent ones of Blochmann, in which a luminous gas flame was rendered non-luminous by the introduction of gases indifferent to combustion, in place of air, have been modified by Wibel in such a way as to permit the heating of the mixed gases at the moment of combustion. The diluting gas was introduced through a glass tube, soldered into one of the draughtholes of the ordinary Bunsen burner, the others being closed, and the mixed gases were burned from a platinum tube, readily formed by rolling a piece of thin platinum foil spirally, slipped into the top of the burner. Two opposite horizontal - Bunsen burners were arranged for heating this tube. Upon heating it when the flame was rendered non-luminous by air, as in the ordinary Bunsen burner, or by carbonic acid, nitrogen, or hydrogen, Wibel noticed the immediate formation of a luminous cone in the interior of the flame, which gradually disappeared when the heating burners were removed. The temperature required was not very high, especially if the gases were mixed in the proper proportions. The flame did not strike down, and in all respects resembled an ordinary luminous flame, affording soot, and also a continuous spectrum. Very slight decomposition took place in the hot tube with nitrogen and carbonic acid, as ascertained by analysis of gas taken from the flame by aspiration, as well as from the exceedingly slight deposit of carbon in the tube. A sheet-iron plate, perforated so as to fit the burner, prevented the products of combustion from the heating burners from coating the flame. It was also found that when the flames of two good Bunsen burners were brought in contact with the exterior mantle of flame, rendered non-luminous by carbonic acid, an interior luminous cone was formed, which disappeared immediately on their removal. He concludes from his experiments that the non-luminous character of the flame in Knapp's experiment is not due to dilution of the burning gas, according to the views of Frankland and of Blochmann, but rather to a cooling of the interior of the flame by the gas introduced a view that is supported by the peculiarities of the flame when oxygen is the diluting gas. The luminosity of the flame of a substance containing carbon, other things

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