It was Hertz’s task—following up Maxwell’s prediction—to devise an instrument which would detect waves not cognizable by our senses alone. For this purpose he used a simple loop of wire with the ends brought near together, each terminating in a metal ball. When these balls were brought almost into contact, a small electrical spark was seen to pass between the balls when the “oscillator”—the apparatus used to generate the oscillating currents, or electric waves, of high frequency—was set in operation.[37] Hertz not only proved that the speed of electric waves is the same as that of light, and that they are subject, under certain conditions, to “interference” as are light-waves, but he also succeeded in actually measuring the length of the waves produced by his crude apparatus. This was accomplished by producing what are known as “standing waves,” analogous to the sound-waves produced by an organ-pipe. Moving his detector slowly along the wire, Hertz observed that the spark would appear when a certain interval of space was reached, and as he continued to move the detector the sparks would disappear and reappear at regular distances. He rightly concluded that these points of disappearance and reappearance of the spark corresponded to the nodes and loops of the “standing waves,” representing the wave-length of the electrical undulations. It has since been established that the difference in wave-length between the electric undulations produced by Hertz and those of light-waves may be enormous or quite moderate. Professor Michelson tells us that “a telegraphic wave”, which is practically an electromagnetic disturbance, may be as long as 1000 miles. The waves produced by the oscillations of a condenser, like a Lyden jar, may be as short as 100 feet; the waves produced by a Hertz oscillator may be as short as one-tenth of an inch. Between this and the longest light-wave there is not an enormous gap, for the latter has a length of about 1/1000 inch. Thus the difference between the Hertz vibrations and the longest light-wave is less than the difference between the longest and shortest light-waves, for some of the shortest oscillations are only a few millionths of an inch long. Doubtless even this gap will soon be bridged over.[38] The Hertz apparatus was greatly improved by Auguste Righi, in the University of Bologna. In the same class in physics was Marconi, who began his fruitful experiments in 1895, one year after Sir Oliver Lodge had perfected the coherer. Lodge’s coherer, used by Marconi in his early work, consisted of a glass tube containing a pinch of nickel and silver filings in equal parts. Crude as this detector was, judged by present-day standards, it materially improved the conductivity of contact metals in the case of Hertzian waves.