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Ring-and-spring microphones, such as this Western Electric microphone, were common during the electrical age of sound recording c. 1925–45.. The second wave of sound recording history was ushered in by the introduction of Western Electric's integrated system of electrical microphones, electronic signal amplifiers and electromechanical recorders, which was adopted by major US record labels in ...
Heinrich Rudolf Hertz (1856–1894) proved the existence of electromagnetic radiation. In an 1864 presentation, published in 1865, James Clerk Maxwell proposed theories of electromagnetism and mathematical proofs demonstrating that light, radio and x-rays were all types of electromagnetic waves propagating through free space.
Before the discovery of electromagnetic waves and the development of radio communication, there were many wireless telegraph systems proposed and tested. [4] In April 1872 William Henry Ward received U.S. patent 126,356 for a wireless telegraphy system where he theorized that convection currents in the atmosphere could carry signals like a telegraph wire. [5]
As the gaps made and broke contact, the radio wave was audible as a tone in a crystal set. The telegraph key often directly made and broke the 2000 volt supply. One side of the spark gap was directly connected to the antenna. Receivers with thermionic valves became commonplace before spark-gap transmitters were replaced by continuous wave ...
In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimeters (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges, allowing some to even hear ultrasounds
It’s one of many historical inventions that were way ahead ... The toad indicated the direction the seismic wave was traveling. ... a 3,000-year-old rock crystal discovered in 1850 at the ...
The terms quasi-optical waves and ultrashort waves were used briefly [37] but did not catch on. The first usage of the word micro-wave apparently occurred in 1931. [ 39 ] [ 40 ]
The scientists discovered an object 15,000 light-years from Earth in the Scutum constellation. The object, dubbed GPM J1839−10, released radio waves every 22 minutes. The bursts of energy lasted ...