FIG. 2_a_ represents a more complete electrical arrangement of the receiver circuit. The vertical wire, W', is connected to one wire of the coherer, L. The other wire of the coherer is led to the ground, G. The wires in the coherer, L, are separated by fine metallic particles. B represents a battery. E, an electro-magnet which attracts a piece of iron, A (armature), and closes a local battery, B, causing a click of the sounder (electro-magnet), S. The magnetic waves (Fig. 5) embracing the wire, W', cause a pulsation in this wire which produces an electrical disturbance in the coherer analogous to that shown in Fig. 3, by means of which an electrical current is enabled to pass through the electro-magnet, E.] In the photographs of these magnetic whirls, Fig. 4 is the whirl produced in the circuit C' by the battery B (Fig. 2), while Fig. 5 is that produced by electrical sympathy, or as it is called induction, in a neighboring wire. These photographs were obtained by passing the circuits through the sensitive films, perpendicularly to the latter, and then sprinkling very fine iron filings on these surfaces and exposing them to the light. In order to obtain these photographs a very powerful electrical current excited the coil C (Fig. 2), and the neighboring circuit W' (Fig. 5) was placed very near the circuit W. When the receiving wire is at the distance of several miles from the sending wire it is impossible to detect by the above method the magnetic ripples or whirls. We can, however, detect the electrical currents which these magnetic lines of force cause in the receiving wire; and this leads me to speak of the discovery of a remarkable phenomenon which has made Marconi's system of wireless telegraphy possible. In order that an electrical current may flow through a mass of particles of a metal, a mass, for instance, of iron filings, it is necessary either to compress them or to cause a minute spark or electrical discharge between the particles. Now, it is supposed that the magnetic whirls, in embracing the distant receiving circuit, cause these minute sparks, and thus enable the electric current from the battery B to work a telegraphic sounder or bell M. The metallic filings are inclosed in a glass tube between wires which lead to the battery, and the arrangement is called a coherer. It can be made small and light. Fig. 6 is a representation in full size of one that has been found to be very sensitive. It consists of two silver wires with a few iron filings contained in a glass tube between the ends of the wires. It is necessary that this little tube should be constantly shaken up in order that after the electrical circuit is made the iron filings should return to their non-conducting condition, or should cease to cohere together, and should thus be ready to respond to the following signal. My colleague, Professor Sabine, has employed a very small electric motor to cause the glass tube to revolve, and thus to keep the