December 10, 1915] 



SCIENCE 



811 



its position of equilibrium. Increase the 

 tension until the string d breaks when the 

 displaced steel tongue is released; it will 

 then return to its normal position after per- 



forming a few oscillatory movements. The 

 analogy between the motion of the steel 

 tongue and the motion of electricity 

 referred to above is quite complete and to 

 make it even more complete I attach a card- 

 board disc G which by transferring a con- 

 siderable part of the motion of the tongue to 

 the surrounding air will accelerate the 

 dying out of the oscillatory motion of the 

 tongiie by the transference of the energy 

 of the vibrating cardboard to the surround- 

 ing air. Here is a tuning fork which I 

 pluck with my fingers instead of employing 

 the tension of the string, or which is still 

 better, I give it a gentle impulse with a soft 

 hammer. After each impulse the fork 

 oscillates, imparting some of its motion to 

 the surrounding air, and the vibratory 

 motion of the air propagated in all direc- 

 tions impinges upon your auditory organs 

 and thereby produces in your consciousness 

 the sensation of sound. In the same manner 

 the vibratory motion of electricity in the 

 antenna is communicated to the electricity 

 near the surface of the earth, causing it to 

 move in the same vibratory fashion; these 

 vibrations spread out in all directions and 



travel along the surface with the velocity 

 of light, that is, about 180,000 miles a 

 second. This propagation along the surface 

 of the earth of the oscillatory motion of 

 electricity is called electrical wave motion, 

 just as the propagation of the vibratory 

 motion of the tuning fork through the air 

 is called wave motion. Just as the sound 

 waves produced by the vibration of the tun- 

 ing fork or by my vocal cords spread out in 

 every direction, getting feebler as they 

 progress further and further, but produc- 

 ing a sensation of sound in every healthy 

 ear which they find anywhere, so the prop- 

 agation of the vibratory motion of electric- 

 ity along the surface of the earth spreads 

 out in every direction, getting feebler as it 

 advances further from the sending antenna, 

 but producing a definite effect in every up- 

 right wire like B in Fig. 3, which effect can 

 be detected very clearly by a suitable elec- 

 trical instrument connected with the wire B. 

 This, briefly stated, is wireless transmission 

 of electrical signals. 



We often hear that wireless transmission 

 is only a practical application of electrical 

 waves discovered by a German, the late 

 Professor Hertz; that it is an art which 

 formed its first roots in German soil, 

 whereas in reality it is a particular 

 case of the oscillatory motion of electri- 

 city discovered by Joseph Henry and the 

 laws of which were formulated by Kelvin. 

 It is true that Hertz employed these oscilla- 

 tions more skilfully than anybody else ever 

 did prior to his time, and thereby succeeded 

 improving experimentally the complete va- 

 lidity of the physical foundation of the great 

 electromagnetic theory which was conceived 

 and formulated by Clerk Maxwell, the great 

 Scotch physicist. It is also true that 

 Guglielmo Marconi in 1895, when a mere 

 youth of twenty-one, fascinated by the 

 beauty of the Hertzian experiments, was 

 busy with Hertzian electrical oscillators 



