A paper on wireless telegraphy, Nov. 1905

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cell and galvanometer; he found that the resistance of the tube was nearly infinite, provided the filings were not too tightly squeezed; but when the waves were thrown on the tube, the resistance of it suddenly fell to a few Ohms, and an electric current flowed through the circuit. I show a rough diagram of his coherer circuit. And he found that if the tube was gently tapped, when the waves had ceased, the resistance of it went back to its original high value. In 1894, at Oxford, he showed how he automatically decohered his coherer. I show one of the original forms of decoherer which were used at that time; here a bell is used to detect the waves, which, when it rings, taps the tube and prepares it for the next flow of waves.

The current which passed through the

G. Diagram of completed Receiver.

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coherer did not usually ring the bell, because a fairly large current is required for this, so this small current worked a relay which was connected to a large battery in circuit with the bell or other instrument. I show this relay method. About 1896 Prof. Ernest Wilson carried on a number of experiments on wireless telegraphy in the Siemen's Laboratory, K.C.L. He invented and patented a new kind of coherer, the "Magnetic Detector", which is a self-decohering coherer. The impulses from the receiving aerial pass through the primary of a small transformer, with an iron core, the secondary of which is connected to a telephone receiver. In doing so they alter the magnetism of the core and hence induce a temporary current in a telephone. A permanent magnet is kept in contin-

14. Signor Marconi ; Portrait.

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ual motion near the transformer core, which restores the magnetism to its original state immediately after the impulses have been received. The moving magnet thus performs the same function as the tapper in the tube coherer receiver. The messages are read by the sound of the dots and dashes in the Telephone.

In 1895 G. Marconi designed and constructed an apparatus in which the transmitter consisted of a Hertzian radiator, i.e. two short metal cylinders between which an electric charge was allowed to discharge, placed in a focal line of a parabolic mirror, using Lodge's glass tube coherer and automatic decoherer. Between 1894 & 1896 Marconi gave great attention to all kinds of improvements of devices for the detection of electric waves. He made a new