WIRELWSS TELEPHONY.

Dominion, Volume 2, Issue 571, 28 July 1909, Page 3

WIRELWSS TELEPHONY.

—: o— ——• LESSONS OF SOME RECENT RE- . SEARCHES. ~.-.■ Some curious facts concerning radio-tele-graphy were' mentioned at the Royal.lnstitution recently ( in an address by Professor J.: A. Fleming, .Pender Professor of Electrical Engineering at the- London ,Uniyersity. It has, long been known that radiotelegraphy is conducted with greater facility over,sea than over land, and part of.the lecture' was an exposition of recent investigations into the caUses"of the'difference.- It was shown -by: a simple experiment with-' iron, copper, and galvanised .iron'spirals that a zinc-covered or galvanised-iron , wire con- - ducts high frequency, oscillations almosfc'.as well.as. a copper wire, .but: that if the zinc skill is burnt off the wire then acts as an ordinary;'.'iron'-wire. 'This' proves'-'that the high-frequency, currents are confined to a surface slqn. Curves were exhibited derived, from a recent research, by Dr. Zenneck,' of .Brunswick, showing the! relative effect of sea water, fresh water, damp soil, and dry soil.

The ;curious and marked property of carborundum, and,molybdenite of conducting electricity better in'one ■[direction than another was discussed) and Dr."Fleming exhibited experiments with a new detector of his own,'consisting of an incandescent lamp with a, metallic filament of tungsten, havini a copper cylinder around, but not touching it. ."[Reference 'was made to "the problem of wireless telephony. It was shown that by means- of :;&©• recently-invented oscillation detectors, articulate speech, and not merely signals, could b'o transmitted, provided that the antenna was made to radiate persistent or; undamped waves. Some of the newor methods of producing these oscillations were considered,' including the high, tension aluminium arc of Ernst Ruhiner.