of larger size, but still very small, (1830.) This gentleman was not slow to apply his skill to the generation of motion, and a successful attempt of his, is recorded in this journal, vol. xx. p. 340. A power was thus applied to the movement of a machine, by a beam suspended in the centre, which performed regular vibrations in the manner of a beam of a steam engine. This is the original application from which have sprung, or at least to which have succeeded, several similar attempts, both in this country and in Europe. A galvanic machine was reported to the British Association, in 1835, by Mr. McGauly, of Ireland, and he has renewed his statements of successful experiments, at the late meeting at Bristol. Mr. Sturgeon of Woolwich, England, also reports a galvanic machine as being in use on his premises for pumping water, and for other mechanical purposes.* But, I believe that Mr. Davenport, named at the head of this notice, has been more successful than any other person in the discovery of a galvanic machine of great simplicity and efficiency. During the last two or three years, much has been said of this discovery in the newspapers, and it is probable that in a future number of this Journal, drawings and an accurate description of the machine may be given. Having been recently invited to examine a working model, in two varieties of form, and to report the result, I shall now attempt nothing more than a general description, such as may render intelligible the account I am to give. 1. The Rotary Machine, composed of Revolving ElectroMagnets, with Fixed Permanent Magnets. This machine was brought to New-Haven, March 16, 1837, by Mr. Israel Slade of Troy, N. Y., and by him set in motion for my examination. The moving part is composed of two iron bars placed horizontally, and crossing each other at right angles. They are both five and a half inches long, and they are terminated at each end by a segment of a circle made of soft iron; these segments are each three inches long in the chord line, and their position, as they are suspended upon the ends of the iron bars, is horizontal. * Sturgeon's Annals of Electricity, Magnetism, &c., No. I. Vol. I., Oct. 1836. Mr. Sturgeon remarks, that, as he thought it might be improved, the machine has long since been laid by. - Compiler. † Mr. Davenport appears to have been strictly the inventor of a method of applying galvanism to produce rotary motion. This iron cross is sustained by a vertical axis, standing with its pivot in a socket, and admitting of easy rotation. The iron cross bars are wound with copper wire, covered by cotton, and are made to form, at pleasure, a proper connexion with a circular battery, made of concentric cylinders of copper and zinc, which can be immersed in a quart of acidulated water. Two semicircles of strongly magnetized steel, form an entire circle, interrupted only at the two opposite poles, and within this circle, which lies horizontally, the galvanized iron cross moves in such a manner that its iron segments revolve parallel and very near to the magnetic circle, and in the same plane. Its axis at its upper end, is fitted by a horizontal cog-wheel to another and larger vertical wheel, to whose horizontal axis weight is attached and raised by the winding of a rope. As soon as the small battery, destined to generate the power, is properly connected with the machine, and duly excited by diluted acid, the motion begins, by the horizontal movement of the iron cross, with its circular segments or flanges. By the galvanic connexion, these crosses and their connected segments are magnetized, acquiring north and south polarity at their opposite ends, and being thus subjected to the attracting and repelling force of the circular fixed magnets, a rapid horizontal movement is produced, at the rate of two hundred to three hundred revolutions in a minute, when the small battery was used, and over six hundred with a calorimotor of large size. The rope was wound up with a weight of fourteen pounds attached, and twenty-eight pounds were lifted from the floor. The movement is instantly stopped by breaking the connexion with the battery, and then reversed by simply interchanging the connexion of the wires of the battery with those of the machine, when it becomes equally rapid in the opposite direction. The machine, as a philosophical instrument, operates with beautiful and surprising effect, and no reason can be discovered why the motion may not be indefinitely continued. It is easy to cause a very gradual flow of the impaired or exhausted acid liquor from, and of fresh acidulated water into, the receptacle of the battery; and whenever the metal of the latter is too much corroded to be any longer efficient, another battery may be instantly substituted, and that even before the connexion of the old battery is broken. As to the energy of the power, it becomes at once a most interesting inquiry, whether it admits of indefinite increase? To this inquiry it may be replied, that provided the magnetism of both the revolving cross and of the fixed circle can be indefinitely increased, then no reason appears why the energy of the power cannot also be indefinitely increased. Now, as magnets of the common kind, usually called permanent magnets, find their limits within, at most, the power of lifting a few hundred pounds, it is obvious that the revolving galvanic magnet must, in its efficiency, be limited, by its relation to the fixed magnet. But it is an important fact, discovered by experience, that the latter is soon impaired in its power by the influence of the revolving galvanic magnet, which is easily made to surpass it in energy, and thus, as it were, to overpower it. It is obvious, therefore, that the fixed magnet, as well as the revolving, ought to be magnetized by galvanism, and then there is every reason to believe that the relative equality of the two, and of course their relative energy, may be permanently supported, and even carried to an extent much greater than has been hitherto attained. 2. Rotating Machine, composed entirely of Electro-Magnets, both in Fixed and Revolving Members. A machine of this construction has been this day, March 29, 1837, exhibited to me by Mr. Thomas Davenport, himself, who came from New-York to New-Haven for that purpose. It is the same machine that has already been described, except that the exterior fixed circle is now composed entirely of electro-magnets. The entire apparatus is therefore constructed of soft unmagnetic iron, which being properly wound with insulated copper wire, is magnetized in an instant, by the power of a very small battery. The machine is indeed the identical one used before, except that the exterior circle of permanent magnets is removed, and in its place is arranged a circle of soft iron, divided into two portions to form the poles. These semicircles are made of hoop-iron, one inch in width, and one eighth of an inch in thickness. They are wound with copper wire, insulated by cotton-covering about ten inches in length on each semicircle and returning upon itself by a double winding, so as to form two layers of wire, making on both semicircles about one thousand and five hundred inches. The iron was not wound over the entire length of one of the steel semicircles; but both ends were left projecting, and being turned inward, were made to conform to the bend of the other part; each end that is turned inward and not wound is about one third of the length of the semicircle. These semicircles being thus fitted up, so as to become at pleasure, galvanic magnets, were placed in the same machine that has been already described, and occupied the same place that the permanent steel magnets did before. The conducting wires were so arranged, that the same current that charged the magnets of the motive wheel, charged the stationary ones, placed around it, only one battery being used. It should be observed, that the stationary galvanic magnets, thus substituted for the permanent steel ones, were only about half the weight of the steel magnets. This modification of the galvanic magnet is not, of course, the best form for efficiency; this was used merely to try the principle, and this construction may be superseded by a different and more efficient one. But with this arrangement, and notwithstanding the imperfection of the mechanism of the machine, --when the battery, requiring about one quart of diluted acid to immerse it, was attached, it lifted 16lbs. very rapidly, and when the weight was removed, it performed more than 600 revolutions per minute. So sensible was the machine to the magnetic power, that the immersion of the battery one inch into the acidulated water, was sufficient to give it rapid motion, which attained its maximum when the battery was entirely immersed. It appeared to me that the machine had more energy with the electro-magnets than with those that were permanent; for, with the smallest battery, whose diameter was three inches and a half, its height five inches and a half, and the number of concentric cylinders, three of copper and three of zinc, the instrument manifested as great power as it had done with the largest batteries, and even with a large calorimotor, when it was used with a permanent instead of a galvanic magnet. With the small battery, and with none but electro or galvanic magnets, it revolved with so much energy as to produce a brisk breeze, and powerfully to shake a large table on which the apparatus stood. Although the magnetization of both the stationary and revolving magnets was imparted by one and the same battery, the magnetic power was not immediately destroyed, by breaking the connexion between the battery and the stationary magnet; for, when this was done, the machine still performed its revolutions with great, although diminished, energy; in practice, this might be important, as it would give time to make changes in the apparatus, without stopping the movement of the machine. It has been stated by Dr. Ritchie, in a late number* of the London and Edinburgh Phil. Magazine, that electro-magnets do not attract at so great a distance as permanent ones, and therefore are not well adapted for producing motion. On this point, Mr. Davenport made the following experiment, of which I was not a witness, but to which I give full credit, as it was reported to me by Mr. Slade, in a letter, dated NewYork, March 24, 1837. Mr. Davenport suspended a piece of soft iron with a long piece of twine, and brought one pole of a highly charged steel magnet within the attracting distance, that is, the distance at which the iron was attracted to the magnet; by measure * January, 1837. |