From this description it is very easy to see how the system works.  Let us suppose, in fact, that the current which is traversing the spirals of the helix, r, has a direction such that the helix in its movement approaches the pole, S; then the prolongation, v, will uncover the slit, a, which, along with a’, had up to this moment been closed, and a luminous fascicle escaping through a will strike the lens, l’, and from thence converge upon the selenium plates, z’.  This is all the duty that the line current has to perform.

The luminous rays, in falling upon the selenium plates, z’, modify the resistance that these offered to the passage of the current produced by the battery, B’.  As this resistance diminishes, the intensity of the current in the circuit supplied by the battery, B’, increases, the attractive action of the polar pieces of the magnet, M’, diminishes, the equilibrium is destroyed, and the piece, A, revolves around the axis, i.  If the polarity of the line current were different, the same succession of phenomena would occur, save that the direction of A’s rotation would be contrary.  As for the rheostats, W W’, their object is to correct variations in the selenium’s resistance and to balance the resistances of the two corresponding circuits.  The magnet, A, will be combined with a registering apparatus so as to directly or indirectly actuate the printing lever.  The entire first part of this apparatus, which is very sensitive, may be easily protected from all external influence by placing it in a box, and, if need be, in a room distant from the one in which the employes work.

[Illustration:  FIGS. 3 AND 4.]

The differenzialrecorder alone has to be in the work room.

As may be seen, the system is not wanting in originality.  Experience alone will permit of pronouncing upon the question as to whether it is as practical as ingenious.—­La Lumiere Electrique.

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A NEW CIRCUIT CUTTER.

Messrs. Thomson & Bottomley have recently invented a peculiar circuit cutter based upon the use of a metal whose melting point is exceedingly low.  Recourse is had to this process for breaking the current within as short a time as possible.  In this new device the ends of the conductors are soldered together with the metal in question at one or several points of the circuit.  The metal employed is silver or copper of very great conductivity, seeing that the increase of temperature in a conductor, due to a sudden increase of the current, is inversely proportional to the product of the electric resistance by the specific heat of the conductor; that these metals are best adapted for giving constant and definite results; and that the contacts are better than with lead or the other metals of low melting point which are frequently employed in circuit cutters.