coherer

A coherer is a primitive device used for detecting radio waves. It consists of a tube filled with metal filings placed between two electrodes. When radio waves strike the coherer, they cause the metal filings to clump together, decreasing the electrical resistance of the tube. This decrease in resistance allows a current to flow, which can then be detected by a measuring instrument.

The coherer was a crucial component in early radio communication. It was invented by Jagadish Chandra Bose in the 1890s and later improved upon by Guglielmo Marconi. Marconi's coherer played a significant role in his experiments with long-distance wireless telegraphy. The device's sensitivity to radio waves made it possible to transmit and receive signals over distances previously thought impossible.

However, coherers had several limitations. They were not very stable and could be affected by external vibrations or temperature changes. They also tended to "stick" after detecting a signal, meaning they would remain in a low-resistance state until manually reset. This made it difficult to receive a continuous stream of signals. Despite these drawbacks, the coherer was a vital stepping stone in the development of modern radio technology. It paved the way for more sophisticated detectors that would eventually replace it.