T HE studies pursued in a wireless laboratory are mainly of two kinds : first, those directed to the solution of problems that have arisen in the development or use of practical apparatus, and, secondly, those with which we are here concerned, aiming at the application of novel principles or novel physical phenomena to the invention of new methods or apparatus. Little will be said of the methods of wireless communication as they exist today ; on the contrary, our attention will be devoted to some possibilities of wireless telegraphy-possibilities tested in the laboratory but not yet tried on the large scale. In other words, no attempt will be made to give a record of technical progress accomplished to date but, rather, to discuss wireless communication as it may be. The new methods to be first described are based upon the phenomena, not yet fully known in detail, which occur when one vibrating body is caused to influence the vibrations of another. Consider the case of a simple pendulum consisting of a weight tied to the lower end of a string the upper end of which is held in the hand, and suppose it is of such a length that it would vibrate freely to and fro in a period of two seconds, when the hand is held still. Then it is easily

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Oscillations generated by Three-electrode Thermionic Tubes. 455 (5) A series of light aluminium alloys has been tested with the balance, and it has been found that, whereas the susceptibility of commercial aluminium is increased by alloying with copper and manganese, it is diminished by alloying with cobalt.(6) In a note on the susceptibility of glass in relation to composition it is shown that the balance could be used to rapidly determine the relative amounts of ferrous iron in different specimens of glass.(7) Certain specimens of tourmaline have been examined. The green and dark blue opaque varieties have susceptibilities in the direction of the principal crystallographic axis varying from 16 to 20 per cent, less than in a direction at right angles thereto. The susceptibility of rose-coloured tourma line is very small in comparison.(8) The paper concludes with a note on the retentivity of rock specimens and its possible influence upon magnetic disturbances in magnetic survey work.

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WHEN an electric current is caused to pass across the interface between a pair of conducting masses, heat is in general liberated or absorbed in accordance with the law of Peltier. When the masses are in contact over a, very small area, as, for example, when a cylinder of graphite is laid across a copper wire, there may be, in addition, appreciable generation of heat in accordance with the law of Joule. If the substances constituting the contact are bad conductors of electricity and of heat, and if they stand far apart in the thermoelectric series, the phenomena arising when a current is forced across the joint become very striking, for in such circumstances relatively large amounts of heat may be developed, the heat is conserved, and therefore the thermoelectric effects enhanced.