For another method, Chaffee has developed apparatus by which the power tube operation can be tested at the ordinary, household, current frequency of 60 cycles, for which electrical measuring instruments are standard and extremely accurate.

Hitherto, meaningful tests of the tubes could be made only at the extremely high frequencies of thousands of cycles per second, under which they operate in broadcasting. At these high frequencies, electrical measuring equipment is often erratic and unreliable.

Finally, from his experiments, Chaffee has been able to formulate theories of power tube operation, from which actual performance can be predicted far more accurately than ever before.

Professor Chaffee's techniques are applicable not only to broadcasting tubes, but also throughout the electrical industry, wherever these electric "valves" are employed.

Capable of amplifying current, altering wave shapes and frequencies, detecting electric impulses, oscillating, rectifying current, and many other duties, these modern "magic lamps," first utilized thirty years ago, now have hundreds of uses in industry, research, and entertainment.

"Repeater" tubes are used to magnify the voice thousands of times in long-distance telephoning; sound movies, the "electric eye," remote control devices, X-ray, and television are all applications of the vacuum tube.

Throughout the scientific world, in physics, chemistry, medicine, and other fields, the tubes are used wherever delicate and complex control of electricity is required.

The underlying principle of the vacuum tube, first detected by Edison during his experiments with electric light a half century ago, is that when two wires, one positively charged, and the other negatively, are inserted into a vacuum, and the negative wire or filament is heated, a current passes from the filament through the void to the positive terminal.

His observation that current would pass in only this one direction through the tube was first put to work thirty years ago by J. A. Fleming, an English physicist, who saw a possible use for this feature in the detection and rectifying of radio signals, then being pioneered by Marconi.

The rough control over current, which electricians were able to exercise through changing the potentials on the positive and negative terminals of the original tubes, was rendered extremely sensitive and intricate with the addition, by Dr. Lee De Forest, of an independently charged grid of wire between the heated filament and the positively charged plate.