Nikola Tesla Quote
Alternate currents, especially of high frequencies, pass with astonishing freedom through even slightly rarefied gases. The upper strata of the air are rarefied. To reach a number of miles out into space requires the overcoming of difficulties of a merely mechanical nature.
"Experiments With Alternate Currents Of High Potential And High Frequency" an address to the Institution of Electrical Engineers, London (February 1892)