SCIENTIFIC PAPERS AND ABSTRACTS. CHEMICAL AND MECHANICAL EFFECTS OF STEAM. (Proceedings of the Albany Institute, vol. 1, p. 30.)* Joseph Henry read a communication on the chemical and mechanical effects of steam, with experiments designed to illustrate the great reduction of temperature in steam of high elasticity when suddenly expanded. REFRIGERATION BY RAREFACTION OF AIR. (Proceedings of the Albany Institute, vol. I, p. 39.) March 2, 1825. Joseph Henry read a communication on the production of cold by the rarefaction of air, accompanied with experiments. One of these experiments most strikingly illustrated the great reduction of temperature which takes place on the sudden rarefaction of condensed air. Half a pint of water was poured into a strong copper vessel, of a globular form, and having a capacity of five gallons-a tube of one-fourth of an inch in caliber, with a number of holes near the lower end *[The "Transactions of the Albany Institute," vol. I, part i, is dated on page 3, "June, 1828." The title page of the volume bears date "1830." Part ii of same volume is an "Appendix" of 74 (independently numbered) pages, and comprises brief abstracts of proceedings; here cited as "Proceedings" for conciseness.] and a stop-cock attached to the other extremity, was firmly screwed into the neck of the vessel; the lower end of the tube dipped into the water, but a number of the holes were above the surface of the liquid, so that a jet of air mingled with water might be thrown from the fountain. The apparatus was then charged with condensed air, by means of a powerful condensing pump, until the pressure was estimated at nine atmospheres; during the condensation the vessel became sensibly warm. After suffering the apparatus to cool down to the temperature of the room, the stop-cock was opened; the air rushed out with great violence, carrying with it a quantity of water, which was instantly converted into snow; after a few seconds the tube became filled with ice, which almost entirely stopped the current of air. The neck of the vessel was then partially unscrewed, so as to allow the condensed air to rush out around the sides of the screw; in this state the temperature of the whole atmosphere was so much reduced as to freeze the remaining water in the vessel; the stop-cock and tube at the same time became so cold that the fingers adhered to them, in the same manner that they are sometimes found to stick to the latch of a door on an intensely cold morning. This experiment was exhibited to the Institute within six feet of a large stove, and in a room the temperature of which was not less than eighty degrees of Fahrenheit's thermometer. LECTURE ON FLAME. (Proceedings of the Albany Institute, vol. 1, p. 59.) March 21, 1827. Mr. Joseph Henry delivered a lecture on flame, accom panied with experiments. ON SOME MODIFICATIONS OF THE ELECTRO-MAGNETIC APPA RATUS. (Transactions of the Albany Institute, vol. I, pp. 22–24.) Read October 10, 1827. The subject of electro-magnetism, although one of the most interesting branches of human knowledge, and presenting at this time the most fruitful field for discovery, is perhaps less generally understood in this country than almost any other department of natural science. Our popular lecturers have not availed themselves of the many interesting and novel experiments with which it can so liberally supply them; and, with a few exceptions, it has not as yet been admitted as a part of the course of physical studies pursued in our higher institutions of learning. A principal cause of this inattention to a subject offering so much to instruct and amuse is the difficulty and expense which formerly attended the experiments—a large galvanic battery, with instruments of very delicate workmanship, being thought indispensable. But this bar to the advancement of electro-magnetism no longer exists, several improvements having been made in the principles and arrangement of the apparatus, which tend considerably to simplify its construction and use. Mr. Sturgeon, of Woolwich, who has been perhaps the most successful in these improvements, has shown that a strong galvanic power is not essentially necessary, even to exhibit the experiments on the largest scale. On the contrary, he has proved that it may be almost indefinitely diminished, provided the magnetic force be proportionately increased. On this principle he has constructed a set of instruments, with large magnets and small galvanic elements, which, from their size and the facility of their operations, are well calculated either for the private study or the public lecture room.* Mr. Sturgeon's suite of apparatus, though superior to any other, as far as it goes, does not however form a complete * Annals of Philosophy, new series, vol. 12, page 375. set; as indeed it is plain that his principle of strong magnets cannot be introduced into every article required, and particularly into those intended to exhibit the action of the earth's magnetism on a galvanic current, or the operation of two conjunctive wires on each other. To form therefore a set of instruments, on a large scale, that will illustrate all the facts belonging to this science, with the least expense of galvanisin, evidently requires some additional modification of the apparatus, and particularly in those cases in which powerful magnets cannot be applied. And such a modification appears to me to be obviously pointed out in the construction of Prof. Schweigger's Galvanic Multiplier:* the principles of this instrument being directly applicable to all the experiments in which Mr. Sturgeon's improvement fails to be useful; and to those only can it be successfully applied. The following description of the figures in Plate It will render my meaning sufficiently clear. Fig. 1, is an apparatus on the plan of the Multiplier, to show the deflection of a large magnetic needle. It consists of a coil of wire, A B, of an oblong form, about ten inches in length and one and a half in width, with a small galvanic element attached to each end; the coil is formed of about twenty turns of fine copper or brass wire, wound with silk, to prevent contact, and the whole bound together so as to have the appearance of a single wire. The attachment of the zinc and copper is more plainly shewn in Fig. 2, which *See Green's Electro-Magnetism, page 30. †[The figures, copied from the original copper-plate illustration, are here reproduced in the text for facility of reference.] represents a coil of only two turns of wire: on the left side of the figure the plates are soldered directly to the ends of the wire of the coil; on the right, the plate of zinc Z, is attached to the part of the wire ending with copper on the other side, while the plate of copper on the right corresponds to the zinc on the left. By this arrangement, we can instantly reverse the direction of the currents, and deflect the needle either to the right or left, by merely holding a tumbler of acidulated water so as to immerse one or the other of the double plates into the fluid. The arrows at B, formed of two pieces of card, are intended to show the direction of the currents, and they should point in the course of the wires going from the copper. N S, is the needle, about nine and a half inches long, made by binding together several watch springs, touched separately, so as to form a compound magnet; at the ends are two balls of pith, to show the movement of the needle more plainly. This instrument is complete in itself, and we receive the full effect of the instantaneous immersion of the galvanic element. Figs. Fig. 3, represents a modification of De la Rive's ring on a large scale. A B, is a coil about nine inches by six, with a small cylinder of copper, enclosing another of zinc, without bottoms, soldered to its extremities, which end at c, the whole being suspended by a fibre of raw silk, so as to swing freely in a cup of acidulated water. When this apparatus is made sufficiently light, it invariably places itself, after a few oscillations, at right angles to the magnetic meridian. W and E, are two pieces of card, with letters on them, to show which side of the coil will turn to the east or west: they may be properly placed by recollecting that the current from the copper to the zinc has a tendency to circulate in a direction contrary to that of the sun. |