246 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Physics. 



1. Electrical Waves in Conductors. — In continuation of his 

 work upon electrical waves, or surgings, as Lodge expresses it, 

 Hertz has examined experimentally the theoretical conclusions 

 of Maxwell, Ileaviside, Poynting and others in regard to the dis- 

 tribution of an electrical current upon the surface and through 

 the section of a wire carrying it. It is well known that a steady 

 current distributes itself through the cross section of the con- 

 ductor. When the current however is oscillatory in its nature 

 the distribution ceases to be uniform through the section, and 

 when the current changes its direction many millions of times a 

 second the electricity glides upon the surface of" the conductor or 

 spreads inward from the surface, according to laws analogous to 

 those governing the increase of temperature from the surface of 

 the earth to its interior. The slower the changes of current the 

 deeper the penetration of the electricity into the interior of the 

 wire. Hertz finds the theoretical conclusions fully justified by 

 his experiments. His apparatus was similar to that employed in 

 his earlier researches. Electrical waves of three meters long were 

 produced. Their nodal points were detected by the spark 

 method. In one experiment a space along the wire upon which 

 the electrical oscillations were produced was replaced by two 

 strips of thin metal connected at their ends with the wire. 

 Between them was a stretch of insulated wire with a spark inter- 

 val between the ends. No spark jumped across these ends when 

 the wire was almost entirely surrounded by the tin foil, the wire 

 being then in the center of the conductor. When, however, the 

 smallest portion of the wire was outside, the tin foil sparks ap- 

 peared. In order to make these sparks disappear it was merely 

 necessary to wrap the exposed portion of the wire with tin foil 

 and connect this with the main leading wire. In this case, we 

 have brought the wire back into the interior of the conductor. 

 In another experiment the conductor, which was of very thick 

 copper of 1"5 meters in length, had interposed two metal discs, 

 separated by a short interval. In the interval were two knobs 

 for the passage of sparks. Sparks passed freely when the waves 

 were produced. When, however, the discs were connected by 

 wires passing through corresponding holes in the discs, near the 

 edges and opposite to each other, the spark decreased in length. 

 When wires connected the edges of the discs outside the wires 

 passing through the holes, the sparks decreased still more in 

 length, and when a number of wires connected a number of holes, 

 and wires were placed outside these wires along the edges of the 

 disc, no spark passed in the interior of the cylindrical cage, 

 although the resistance of the exterior wires was greater than the 

 interior wires. The electricity passed along the exterior wires 

 and not through the interior ones. By means of a similar 



