Science: $90 Lightning

Not often do you find an eminent young scientist shopping at the ribbon counter of a 5^ & 10^ store. Yet it was there that 30-year-old Dr. Robert J. Van de Graaff, a Princeton graduate student (on a National Research Council fellowship) purchased the chief sinew of an invention, demonstrated publicly for the first time last week, of which President Karl Taylor Compton of M. I. T. says: “[It] opens up the possibilities of transmutation of the elements on a commercial scale.”

Alchemy’s new keys to transmutation are the alpha particles of electricity which unstable atoms emit and which unsettle other atoms upon collision. Radium emits alpha particles naturally (also betas and .gammas, the latter helpful in cancer). Artificial streams of alpha particles have been produced from vacuum tubes carrying as high as 650,000 volts. But the production of such voltages is expensive. ‘The significance of Dr. Van de Graaff’s purchase at the 5f/ & 10^ store ribbon counter was that he had discovered how to produce a current of electricity with light-ning-like force at a cost (for a small 1,500,000-volt machine) of $90.

The cheap silk ribbon is used as conveyor belts from two small electric generators to two 2-ft. copper spheres mounted on glass rods. The ribbons pass into the spheres through slits and over pulleys on cams within the spheres. At the generators, from copper brushes, the ribbons pick up small charges of electricity, one ribbon positive, the other negative. Entering the copper balls, the electric charges are taken from the ribbon (silk is a less good conductor than copper) and stored on the balls’ copper surfaces. Large voltages accumulate quickly as the ribbons whiz through their slits, silent as the belt on a dentist’s flexible drill arm.

As Dr. Van de Graaff demonstrated his machine last week in a dark laboratory at Princeton, a soft crackling sound was heard, electricity “spilling” from the copper balls in a “corona” effect. Before spilling, each ball had stored 750,000 volts from the whizzing ribbons. The hair of everyone in the room slowly rose and stood on end in the galvanized atmosphere. Then came a sharp report and the spectators’ hair fell back into place as a bright i.500,000-volt shaft of lightning shot from one ball to the other, the overflowing positive and negative charges rushing together. Significance was that this was a steady potential, available until Dr. Van de Graaff turned off his little generators and let the whizzing ribbons come to rest. Surge (alternating) potentials had been made before in great voltages, but at a cost of many thousands of dollars.

Dr. Van de Graaff turned up the lights and smiled into a circle of marveling faces. A few nights later he was to demonstrate his $90 lightning to the American Institute of Physics in Manhattan. After that he was to build a bigger, 10,000,000-volt model of his ribbon-&-copperball generator at M. I. T. He believes 50,000,000 volts may be possible.