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

Excerpt

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....