There is one simple piece of apparatus in the collection, without which telephony and wireless telegraphy would be impossible. To my mind it is the most interesting skeleton there, and if physicists marked the resting places of their apparatus laid to apparent rest and desuetude, this merits the highest sounding and most suggestive inscription. It is called a transformer, and consists merely of two coils of wire placed near each other. One coil is adapted to receive an electric current; the other coil, entirely independent of the first, responds by sympathy, or what is called induction, across the space which separates the coils. Doubtless if man knew all the capabilities of this simple apparatus he might talk to China, or receive messages from the antipodes. He now, by means of it, analyzes the light of distant suns, and produces the singular X rays which enable him to see through the human body. By means of it he already communicates his thoughts between stations thousands of miles apart, and by means of its manifestations I hope to make this article on wireless telegraphy intelligible. My essay can be considered a panegyric of this buried form--a history of its new life and of its unbounded possibilities. [Illustration: FIG. 1.--Disposition of batteries and coils at the sending station, showing the arrangement of the vertical wire and the spark gap.] For convenience, one of the coils of the transformer is placed inside the other, and the combination is called a Ruhmkorf coil. It is represented in the accompanying photograph (Fig. 1), with batteries attached to the inner coil, while the outer coil is connected to two balls, between which an electric spark jumps whenever the battery circuit is broken. In fact, any disturbance in the battery circuit--a weakening, a strengthening, or a break--provided that the changes are sudden, produces a corresponding change in the neighboring circuit. One coil thus responds to the other, in some mysterious way, across the interval of air which separates them. Usually the coils are placed very near to each other--in fact, one embraces the other, as shown in the photograph.