wire connected to an electrostatic condenser definitely 

 produced radio waves, and he devised means for measur- 

 ing the wavelengths of the radio signals. These were found 

 to be of the order of a few meters, corresponding to fre- 

 quencies of about 100 million cycles per second. The 

 generation of powerful radio signals was later achieved 

 by using the triode valve, which could also be used to 

 detect and amplify the weak signals received at a distance 

 from the transmitter. 



With the later discovery of X-rays by Rontgen (1895), 

 which arise when a beam of electrons traversing a vacuum 

 collides with a metal target, thus causing large decelera- 

 tions of the electrons, and the measurement of X-ray wave- 

 lengths by Bragg (1913) — they proved to be of the order 

 of 1/100,000,000 centimeter — it became clear that all these 

 waves (including light waves) were similar in nature. They 

 were all essentially rapidly varying electromagnetic fields, 

 differing in their respective frequencies of variation and 

 wavelengths. Electromagnetic waves are free energy — 

 they will travel through empty space at the maximum 

 speed of 300,000 kilometers per second possible for any 

 physical effect, and all decrease their intensity according 

 to the inverse square of the distance from their source. 

 The finite speed of these waves sets the limit on the rate 

 at which any kind of information can be conveyed by 

 them, and may even set the limit on the size of the ob- 

 servable astronomical Universe. And the finite wavelengths 

 of even the shortest X-rays set a limit on the smallness of 

 detail observable in matter by their use. (But since atomic 

 particles themselves are also associated with very short 

 waves, it is possible to detect even finer details, down to 

 dimensions of the sizes of atomic nuclei, using high energy 

 particles instead of electromagnetic waves). 



53 



