Scientific American Supplement, No. 315, January 14, 1882

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January 14, 1882, by Various

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Title: Scientific American Supplement, No. 315, January 14, 1882

Author: Various

Release Date: May 8, 2006 [EBook #18345]

Language: English

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SCIENTIFIC AMERICAN SUPPLEMENT NO. 315

NEW YORK, JANUARY 14, 1882

Scientific American Supplement. Vol. XIII., No. 315.

Scientific American established 1845

Scientific American Supplement, $5 a year.

Scientific American and Supplement, $7 a year.

THE ELECTRO-MAGNETIC APPARATUS OF DR. PACINOTTI.

In admiring the recent developments of electric science as evidenced by the number of important inventions which have during the past few years been given to the world, especially in those branches of applied science which deal more particularly with the generation of electricity and the production of the electric light, there is often too great a tendency to forget, or, at least, to pass over in comparative silence the claims which the great pioneer workers and discoverers undoubtedly have to a large share of the merit of this scientific development.

It is, of course, obviously impossible in anything approaching a retrospect of the science of magneto-electric induction or its application to illumination to pass slightly over the names of Oersted, of Ampère, of Davy, and of Faraday, but, in other respects, their work is too often lost sight of in the splendid modern developments of their discoveries. Again, there is another group of discoverer-inventors who occupy an intermediate position between the abstract discoverers above named and the inventors and adapters of still more recent times. To this group belong the names of Pixii and Saxton, Holmes and Nollet, Wilde, Varley, Siemens, Wheatstone, and Pacinotti, who was the first to discover a means of constructing a machine capable of giving a continuous current always in the same direction, and which has since proved itself to be the type of nearly all the direct current electric machines of the present day, and especially those such as the Gramme and Brush and De Meritens machines, in which the rotating armature is of annular form; and when it is considered what a large number of the well known electric generators are founded upon this discovery, it must be a matter of general gratification that the recent International Jury of the Paris Exhibition of Electricity awarded to Dr. Antonio Pacinotti one of their highest awards.

The original machine designed by Dr. Pacinotti in the year 1860, and which we illustrate on the present page, formed one of the most interesting exhibits in the Paris Exhibition, and conferred upon the Italian Section a very distinctive feature, and we cannot but think that while all were interested in examining it, there must have been many who could not help being impressed with the fact that it took something away from the originality of design in several of the machines exhibited in various parts of the building.

This very interesting machine was first illustrated and described by its inventor in the Nuovo Cimento in the year 1864, under the title A Description of a Small Electro-Magnetic Machine, and to this description we are indebted for the information and diagrams contained in this notice, but the perspective view is taken from the instrument itself in the Paris Exhibition.

In this very interesting historical communication the author commences by describing a new form of electro-magnet, consisting of an iron ring around which is wound (as in the Gramme machine) a single helix of insulated copper wire completely covering the ring, and the two ends of the annular helix being soldered together, an annular magnet is produced, enveloped in an insulated helix forming a closed circuit, the convolutions of which are all in the same direction. If in such a system any two points of the coil situated at opposite ends of the same diameter of the ring be connected respectively with the two poles of a voltaic battery, the electric current having two courses open to it, will divide into two portions traversing the coil around each half of the ring from one point of contact to the other, and the direction of the current, in each portion will be such as to magnetize the iron core, so that its magnetic poles will be situated at the points where the current enters and leaves the helix, and a straight line joining these points may be looked upon as the magnetic axis of the system. From this construction it is clear that, by varying the position of the points of contact of the battery wires and the coil, the position of the magnetic axis will be changed accordingly, and can be made to take up any diametrical position with respect to the ring, of which the two halves (separated by the diameter joining the points of contact of the battery wires with the coil) may be regarded as made up of two semicircular horseshoe electro-magnets having their similar poles joined. To this form of instrument the name Transversal electro magnet (Eletro calamita transversale) was given by its inventor, to whom is undoubtedly due the merit of having been the first to construct an electro-magnet the position of whose poles could be varied at will by means of a circular commutator.

PACINOTTI ELECTRO-MAGNETIC MACHINE.—MADE IN 1860.

By applying the principle to an electro-magnetic engine, Dr. Pacinotti produced the machine which we illustrate on the present page. The armature consists of a turned ring of iron, having around its circumference sixteen teeth of equal size and at equal angular distance apart, as shown in Fig. 1, forming between them as many spaces or notches, which are filled up by coiling within them helices of insulated copper wire, r r r, in a similar manner to that adopted in winding the Brush armature, and between them are fixed as many wooden wedges, m m, by which the helices are firmly held in their place. All the coils are wound round the ring in the same direction, and the terminating end of each coil is connected to the commencing end of the next or succeeding helix, and the junctions so made are attached to conducting wires which are gathered together close to the vertical shaft on which the armature ring is fixed, passing through holes at equal distances apart in a wooden collar fixed to the same shaft, and being attached at their lower extremities to the metallic contact pieces of the commutator, c, shown at the lower part of Fig. 3, which is an elevation of the machine, while Fig. 4 is a plan of the same apparatus.

The commutator consists of a small boxwood cylinder, carrying around its cylindrical surface two rows of eight holes, one above the other, in which are fitted sixteen contact pieces of brass which slightly project above the surface of the wood, the positions of those in the upper circle alternating or breaking joint with those in the lower, and each contact piece is in metallic connection with its corresponding conducting wire, and, therefore, with the junction of two of the helices on the armature. Against the edge of the commutator are pressed by means of adjustable levers two small brass contact rollers, k k, which are respectively connected with the positive and negative poles of the voltaic battery (either through or independent of the coils of a fixed electro-magnet, to which we shall presently refer), and the magnetic axis of the ring will lie in the same plane as the line joining the points of contact of the battery and rotating helix, this axis remaining nearly fixed notwithstanding the rotation of the iron ring in which the magnetism is induced.

In the apparatus figured in Figs. 3 and 4, the armature rotates between the two vertical limbs, A B, of a fixed electro-magnet furnished with extended pole pieces, A A, B B (Fig. 4), each of which embraces about six of the armature coils. The fixed electro-magnet is constructed of two vertical iron cylindrical bars, A and B, united at their lower extremities by a horizontal iron bar, F F, the one being rigidly and permanently attached to it, while the other is fastened to it by a screw, G, passing through a slot so that the distance of the pole pieces from one another and from the armature ring is capable of adjustment.

The connections of the machine, which are shown in Fig. 3, are made as follows: The positive current, entering by the attachment screw, h, passes by a wire to the right hand commutator screw, l, to the right-hand roller, k, through the commutator to the ring, around which it traverses to the left-hand roller, k¹, and screw, l¹, to the magnet coil, A, and thence through the coil of the magnet, B, to the terminal screw, h, on the right hand of the figure. This method of coupling up is of very great historical interest, for it is the first instance on record of the magnet coils and armature of a machine being included in one circuit, giving to it the principle of construction of