separating them from those which are in the opposite; and he also points our the reversibility of the apparatus, showing that as an electro-magnetic engine it is capable of converting a current of electricity into mechanical motion capable of performing work, while as a magneto-electric machine it is made to transform mechanical energy into an electric current, which in other apparatus, forming part of its external circuit, is capable of performing electric, chemical, or mechanical work.

All these statements are matters of everyday familiarity at the present day, but it must be remembered that they are records of experiments made twenty years ago, and as such they entitle their author to a very distinguished place among the pioneers of electric science, and it is somewhat remarkable that they did not lead him straight to the discovery of the “action and reaction” principle of dynamo-electric magnetic induction to which he approached so closely, and it is also a curious fact that so suggestive and remarkable a paper should have been written and published as far back as 1864, and that it should not have produced sooner than it did a revolution in electric science.—­Engineering.

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THE ELIAS ELECTROMOTOR.

We lately published a short description of a very interesting apparatus which may be considered in some sense as a prototype of the Gramme machine, although it has very considerable, indeed radical differences, and which, moreover, was constructed for a different purpose, the Elias machine being, in fact, an electromotor, while the Gramme machine is, it is almost unnecessary to say, an electric generator.  This apparent resemblance makes it, however, necessary to describe the Elias machine, and to explain the difference between it and the Gramme.  Its very early date (1842), moreover, gives it an exceptional interest.  The figures on the previous page convey an exact idea of the model that was exhibited at the Paris Electrical Exhibition, and which was contributed by the Ecole Polytechnique of Delft in the Dutch Section.  This model is almost identical with that illustrated and described in a pamphlet accompanying the exhibit.  The perspective illustrations show the machine very clearly, and the section explains the construction still further.  The apparatus consists of an exterior ring made of iron, about 14 in. in diameter and 1.5 in wide.  It is divided into six equal sections by six small blocks which project from the inner face of the ring, and which act as so many magnetic poles.  On each of the sections between the blocks is rolled a coil, of one thickness only, of copper wire about 0.04 in. in diameter, inclosed in an insulating casing of gutta percha, giving to the conductor thus protected a total thickness of 0.20 in.; this wire is coiled, as shown in the illustration.  It forms twenty-nine turns in each section, and the direction of winding