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Prof. J. A. Fleming. Conversion of Electric [Jan. 24, 



be the secondary circuit of an air core transformer in which electric 

 oscillations are set up. As is now well known, the vacuous space in 

 the bulb permits negative electricity to move in it from the hot 

 filament or cathode through the vacuous space to the cylinder or anode 

 and back through the galvanometer and coil, but not in the reverse 

 direction, as long as the cylinder is cool and the carbon filament not 

 at a temperature much above the melting point of platinum. To- 

 illustrate the action of the bulb as an electrical valve, the following 

 experiments can be shown : 



Electric oscillations are set up in a metal wire circuit by the discharge 

 of a Leyden jar, as usual. This circuit takes the form of a thick 

 wire of one or more turns, bent into the form of a circle or square. 

 Some distance from this, we place another wire, of several, say eight 



FIG. 1. 



or ten turns, also bent into the form of a circle, and connect this last 

 wire into the circuit of a galvanometer and vacuum bulb made as de- 

 scribed, so that it is a circuit having unilateral conductivity. On exciting 

 the oscillations in the primary circuit by an induction coil we have an 

 alternating high frequency magnetic field produced, which affects the 

 secondary circuit at a distance. The oscillations in this last are, 

 however, able to flow only in one direction. Hence, the galvanometer 

 is acted upon by a series of intermittent but unidirectional electro- 

 motive forces, and its needle or coil deflects. Since the field is a high 

 frequency field, we can show the screening effect of a sheet of tin foil 

 or silver paper in a very simple and effective manner by the effect it 

 produces in cutting down the galvanometer deflection when the metal 

 sheet is interposed between the primary secondary circuits. Also, if 

 we move the secondary coil away from the primary coil or turn the 

 two coils with their planes at right angles to one another, then the 

 galvanometer deflection diminishes or falls to zero because the induc- 

 tion is decreased. Accordingly, we have in this vacuum valve and 



