THE COHERER

This is not exactly a tool. It' s just an interesting experiment. The coherer, that was invented by Calzecchi Onesti in the year 1884, is a glass tube into which was inserted the metal filings extremely fine, usually made up of nickel and iron interposed between two electrodes metal plugs witch close the glass tube from both sides. The electrodes are made from copper or other metal with very good electric conductance. The resistance of this filing between the electrodes normally is very high, then the electric conductivity is practically very small. This resistance is lowered very much when the coherer is invested by an electromagnetic wave, and then in the circuit there is a considerable increase or a complete conductivity of the current that reveals the signal.If we put a small vibration to the coherer the resistance becomes very big again. Marconi used it to make the bell of his first radio receiver in 1894.The current of the power supply must be low to not burn the metal filings in the tube. I don' t know if it is nowadays something useful but it iw a strange experiment so I decided to post it. You can watch how it works in thiw video.
https://youtu.be/9aqiULTSrH8