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1901 Transatlantic Self-Restoring Coherer, by Lieutenant Luigi Solari, Italy, c. 1901

Inventory Number: 96386

Number of documents: 2

Document Type: Miscellaneous Note

Document Heading: Coherer


A coherer (or, sometimes, receiver) was an early form of detector in wireless telegraphy, based around the effect that small particles of metal filings stick together (or 'cohere') when an electric field is present. A coherer circuit consisted of a basic electromagnetic wave detector for various wavelengths and a circuit that obtained signals from modulated radio waves. The coherer then 'decoded' these signals.

A coherer consisted of a glass tube having very fine metallic filings enclosed between two plugs (usually silver) forming a V gap, and is attached to a stem (usually ivory or bone) with a square end. The coherer is usually situated about one-sixteenth of an inch from the de-coherence tapper hammer. On receiving a wireless signal, the metal filings in the coherer become conductive, permitting a weak current to pass through the coherer and the telegraph relay. This brings into action the Morse recorder, which registers a dot or dash as the case may be. The tapper then taps the coherer, causing the filings to de-cohere within the coherer and thus it becomes non-conductive again. The tapper then ceases to function and the coherer is ready for the next wireless signal.

A basic coherer for 'Hertzian waves' (wireless telegraphy) was first developed by a French physicist, Edouard Branly, and was later developed by Oliver Lodge and others. Marconi used a Branly-type coherer is his early wireless telegraphy experiments in Italy.

Document Type: Miscellaneous Note

Document Heading: Technical Details of Self-Restoring Coherer (Inv. Num. 96386)


While referred to as a coherer, its properties are closer to that of a semi-conductor rectifier, with an oxide film on the mercury providing the semi-conductor element. This device was developed by P. Castelli, a signalman in the Italian Navy, and was further modified by Lieutenant Luigi Solari of the Italian Navy, who then presented it to Marconi during a visit to the Lizard station in September 1901. It was subsequently known as the 'Solari' or 'Italian Navy' detector. It was a sensitive detector, but was sometimes erractic in terms of working performance.

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