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During a November 1894 (or 1895[18]) public demonstration at Town Hall of Kolkata, Bose ignited gunpowder and rang a bell at a distance using millimetre range wavelength microwaves.[19] Lieutenant Governor Sir William Mackenzie witnessed Bose's demonstration in the Kolkata Town Hall. Bose wrote in a Bengali essay, Adrisya Alok (Invisible Light), "The invisible light can easily pass through brick walls, buildings etc. Therefore, messages can be transmitted by means of it without the mediation of wires."
