[Eleanor's comment: This is why we don't "hear" ordinary radio and TV signals.] Thus the rate of change (the first derivative) of the waveform of the pulse is a CRITICAL factor in perception. Given a thermodynamic interpretation, it would follow that information can be encoded in the energy and "communicated" to the "listener". Communication has in fact been demonstrated. A. Guy (Note 1), a skilled telegrapher, arranged for his father, a retired railroad telegrapher, to operate a key, each closure and opening of which resulted in a pulse of microwave energy. By directing the radiations at his own head, complex mess- ages via the Continental Morse Code were readily received by Guy. Sharp and Grove (note 2) found that appropriate modu- lation of microwave energy can result in "wireless" and "receiverless" communication of SPEECH. The recorded by voice on tape each of the single-syllable words for digits between 1 and 10. The electrical sine-wave analogs of each word were then processed so that each time a sine wave crossed ZERO REFERENCE IN THE NEGATIVE DIRECTION, a brief pulse of microwave energy was triggered. [Eleanor's comment: This is, in effect a form of what is called pulse-RATE modulation.] By radiating themselves with these "voice modulated" microwaves, Sharp and Grove were READILY able to hear, identify, and distinguish among the 9 words. [Typo?] The sounds heard were not unlike those emitted by persons with artificial larynxes. Communication of more complex words and of sentences was not attempted because the averaged densities of energy required to transmit longer messages would approach the current 10 milliwatts per square centimeter limit of safe exposure. The capability of communicating directly with a human being by "receiverless radio" has obvious potentialities both within and without the clinic. But the hotly debated and unresolved question of how much microwave radiation a human being can safely be exposed to will probably forestall applications within the near future. ... -53-