The coils, however, if placed several miles apart, will still respond to each other if they are made sufficiently large, if they are properly placed, and if a powerful current is used to excite one coil. Thus, by simply varying the distance between the coils of wire we can send messages through the air between stations which are not connected with a wire. This method, however, does not constitute the system of wireless telegraphy of Marconi, which it is the object of this paper to describe. Marconi has succeeded in transmitting messages over forty miles between points not connected by wires, and he has accomplished this feat by merely slightly modifying the disposition of the coils, thus revealing a new possibility of the wondrous transformer. If the reader will compare the following diagram (Fig. 2) with the photograph (Fig. 1), he will see how simple the sending apparatus of Marconi is. [Illustration: FIG. 2.--Diagram of the arrangement of wires and batteries at the receiving station.] S is a gap between the ends of one coil, across which an electric spark is produced whenever the current from the batteries B flowing through the coil C is broken by an arrangement at D. This break produces an electrical pulsation in the coil C', which travels up and down the wire W, which is elevated to a considerable height above the ground. This pulsation can not be seen by the eye. The wire does not move; it appears perfectly quiescent and dead, and seems only a wire and nothing more. At night, under favorable circumstances, one could see a luminosity on the wire, especially at the end, when messages are being transmitted, by a powerful battery B. It is very easy to detect the electric lines which radiate from every part of such a wire when a spark jumps between the terminals S of the coil. All that is necessary to do is to pass the wire through a sensitive film and to develop the film. The accompanying photograph (Fig. 3) was taken at the top of such a wire, by means of a very powerful apparatus at my command. When the photograph is examined with a microscope the arborescent electric lines radiating from the wire, like the rays of light from a star, exhibit a beautiful fernlike structure. These lines, however, are not chiefly instrumental in transmitting the electric pulse across space. There are other lines, called magnetic lines of force, which emanate from every portion of the vertical wire W just as ripples spread out on the surface of placid water when it is disturbed by the fall of a stone. These magnetic ripples travel in the ether of space, and when they embrace a neighboring wire or coil they produce similar ripples, which whirl about the distant wire and produce in some strange way an electrical current in the wire. These magnetic pulsations can travel great distances. [Illustration: