Thinner Than Thin

The imperceptible cushion of air held between a thumb and forefinger when their tips rub gently against each other is thicker than the film of glass with which Westinghouse Lamp Co. is sealing certain of its vacuum tubes. That glass is one five-thousandth of an inch thick. Last week Dr. Charles Morse Slack, the company's research physicist, received its annual $500 award for accomplishing the thin sealing.

The tubes which Dr. Slack seals so thinly are Lenard Ray tubes, invented by learned Professor Philipp Lenard of the University of Heidelberg, 1905 winner of the Nobel Prize in Physics. Professor Lenard's tube, devised in the 1890's when modern physics was germinating, projects cathode rays through a thin aluminum or gold window. It requires a minimum of 70,000 volts to fire those rays through the metal windows. That voltage is expensive and difficult to handle.

Dr. Slack's Westinghouse task was to make more permeable windows. A film of glass would serve, were it stout enough to withstand the suction of the Lenard vacuum tubes. Dr. Slack rounds the end of his vacuum tube until it resembles the butt of a test tube. Then he blows the glass to gossamer thinness. A last step is to exhaust the tube. This creates a knob at the tube's end, a knob so frail that when shattered its glassy film floats in air. so stout that it is as strong as steel. Result is that a pressure of only 30,000 volts is needed to fire the cathode rays out into elements, chemicals, cancers, whatever the experimenter wishes to irradiate.

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