1892.] on Alternate Currents of High Potential arid Frequency. 649 



tliey allow to operate all kinds of devices by connecting the device 

 with only one leading wire to the source. In fact, under certain 

 conditions it may be more economical to supply the electrical energy 

 with one lead than with two. 



An experiment of sj)ecial interest is the running, by the use of 

 only one insulated line, of a motor operating on the principle of the 

 rotating macjnetic field enunciated by the author a few years ago. 

 A simple form of such a motor is obtained by winding upon a lami- 

 nated iron core a primary and close to it a secondary coil, closing 

 the ends of the latter and placing a freely movable metal disk within 

 the influence of the moving field. The secondary coil may, how- 

 ever, be omitted. When one of the ends of the primary coil of the 

 motor is connected to one of the terminals of the high-frequency 

 coil and the other end to an insulated metal plate, which, it should 

 be stated, is not absolutely necessary for the success of the experi- 

 ment, the disk is set in rotation. 



Experiments of this kind seem to bring it within the reach of 

 possibility to operate a motor at any point of the earth's surface 

 from a central source, without any connection to the same except 

 through the earth. If, by means of powerful machinery, rapid varia- 

 tions of the earth's potential were produced, a grounded wire reach- 

 ing up to some height would be traversed by a current which could 

 be increased by connecting the free end of the wire to a body of 

 some size. The current might be converted to low tension and used 

 to operate a motor or other device. The experiment, which would 

 be one of great scientific interest, would probably best succeed on a 

 ship at sea. In this manner, even if it were not possible to operate 

 machinery, intelligence might be transmitted quite certainly. 



In the course of this experimental study special attention was 

 devoted to the heating effects produced by these currents, which are 

 not only striking, but open up the possibility of producing a more 

 efficient illuminant. It is sufficient to attach to the coil terminal a 

 thin wire or filament, to have the temi^erature of the latter percei^tibly 

 raised. If the wire or filament be inclosed in a bulb, the heating 

 effect is increased by preventing the circulation of the air. If the 

 air in the bulb be strongly compressed, the displacements are 

 smaller, the impacts less violent, and the heating effect is diminished. 

 On the contrary, if the air in the bulb be exhausted, an inclosed 

 lamp filament is brought to incandescence, and any amount of light 

 may thus be produced. 



The heating of the inclosed lamp filament depends on so many 

 things of a different nature, that it is difficult to give a generally 

 applicable rule under which the maximum heating occurs. As re- 

 gards the size of the bulb, it is ascertained that at ordinary or only 

 slightly differing atmospheric pressures, when air is a good insulator, 

 the filament is heated more in a small bulb, because of the better 

 confinement of heat in this case. At lower pressures, when air 

 becomes conducting, the heating effect is greater in a large bulb^ 



Vol. XIIL (No. 86.; 2 x 



