Any form of receiver may be used with this arc apparatus. The great advantage of this method is that the arc produces continuous oscillations of constant amplitude, and that the wave-length and frequency of the oscillations are subject to better regulation and control.
Advantages.—The advantages of wireless telephony over wireless telegraphy are many. One is that no skilled operator is required to translate the dot-and-dash signals; for in the latter one hears only long and short buzzes, whereas in the former one hears the actual spoken words. By means of wireless telephony the transmission of intelligence is far more direct and expeditious, and in times of emergency this not unfrequently becomes a very vital question indeed. An important characteristic of wireless telephonic communication is the exceptional clearness of the articulation, owing to the absence of the electrostatic capacity of metallic lines and cables which is always present in wire telephony.
Stronger currents, improved sending and receiving apparatus, and the application of new principles have now greatly extended the speaking range; and only recently distinct communication has been established by wireless telephony between New York and San Francisco. The use of the wireless telephone will be greatly extended, especially in naval, military, and shipping communication.
THE MARVEL OF X-RAYS
Röntgen or X-Rays, the most famous, and up to now by far the most useful, kind of rays associated with high vacuum tubes, were discovered by Professor W. K. Röntgen in 1895. His first observation was that a photographic plate, which was enclosed in an opaque material and which was lying by chance near the apparatus, was affected just as if it had been exposed to ordinary light. This caused him to conclude that the effect must be due to some unknown kind of rays, and the uncertainty as to their character led him to provisionally apply to them the name of X-rays, for x in algebra generally denotes the unknown quantity.
The later sensational part of his discovery was that the property possessed by a highly exhausted bulb of glass, fitted with suitable electrodes, sends out rays or electric discharges capable of passing through many bodies which are quite opaque to ordinary light, and of either affecting a photographic plate or causing a screen coated with certain chemicals to fluoresce or light up under their influence.
How are X-rays produced?
X-rays are thus produced by the discharge of a high-potential current through a special form of vacuum tube, known as a Crookes’ tube. The positive terminal of an induction coil or Wimshurst machine is connected to the anode and the negative to the cathode of the tube. The anticathode is connected to the anode and is also positive. The vacuum of a tube is not perfect, and the current is conveyed through the tube by the infinitesimal quantity of air contained therein.
DIAGRAM SHOWING PARTS OF X-RAY TUBE