Physics & Optics

In Cambridge, Mass, last week, members of the American Physical Society and of the Optical Society of America were given a first look at Massachusetts Institute of Technology's new spectroscopic laboratory. President Karl Taylor Compton of the Institute and Professor George Russell Harrison, who has charge of the new shop, showed the physicists about. The new building is constructed like and really is an icebox. The outer walls--4 ft. thick--are of brick, 8 in. of cork, an air space and concrete. Within that well-insulated casing is an inner structure of ten rooms. The inner building has its own, separate foundations, is further insulated from the outer husk by 6 in. of dead air. Thermostat control and automatic air conditioners maintain the ten rooms of the icebox at any desired temperature and humidity. Year-round humidity will be kept at between 35% and 45%. Temperature will not vary more than one-tenth of one degree from 68DEG F. The constant conditions are essential. For in those rooms Tech men will try to find out more about what all things are made of than man now knows. It is a friendly competition with all other research institutions, but especially with California Institute of Technology. From the white buildings of M. I. T. the visiting physicists and opticians proceeded out tawdry Massachusetts Avenue to the red buildings of Harvard University, to whose professor emeritus of physics, Dr. Theodore Lyman, they gave the Frederick Ives Medal, and where they heard learned discourse. Dr. Albert Wallace Hull of General Electric described two meticulous counters:1) the device of Dr. Merle Anthony Tuve of the Carnegie Institution (TIME, Feb. 8), which measures a current of one electron per second, smallest current measured so far; 2) the device (including thyratron tubes) of Dr. Wynn Williams of Cambridge University, England, which counts alpha particles (nuclei of helium atoms) as they explode from radium at a speed of 12,000 mi. per sec., and ten microseconds apart. (A microsecond is one-millionth of a second.) Dr. Kenneth T. Bainbridge of Bartol Laboratories, Philadelphia, again described his two-ton mass-spectrograph which is sensitive to one-trillionth of a trillionth of an ounce (TIME, Feb. 22), which delicately indicated that the average atomic weight of the isotopes of tellurium is (new observation) 127.47 instead of 127.5. Dr. Bainbridge is proud that his machine cost him only $2,000 to build. President Compton of M. I. T. announced the immediate construction of a 15,000,000-volt x-ray tube and equipment to operate it. Building a tube strong enough to carry that tremendous energy is no great feat. General Electric's Dr. William David Coolidge built one for 900,000 volts. It is now being used to treat cancer in Manhattan's Memorial Hospital. Then there are Caltech's Dr. Charles Christian Lauritsen's for 1,200,000 volts, Carnegie Institution's Dr. Tuve's for 2,000,000. In Berlin last year Drs. F. Lange and A. Brasch sent 2,600,000 volts through a simple tube, are building a bigger one for the 16,000,000 volts which lightning often strikes at their experimental station in the Alps (TIME, June 29). The great problem has been to store up stupendous amounts of electricity which could be sent crashing through stout tubes. If power were great enough physicists are sure that they could propel heavy protons as well as light electrons at naked elements, shatter the toughest of substances. The Germans in the Alps had at their disposal the colossal but unmanageable and undependable lightning. President Compton has the magnificently simple machine which Dr. Robert J. van de Graaff, young Tech research associate, built for $90 and demonstrated to the American Institute of Physics (TIME, Nov. 16). The model accumulated 1,500,000 volts. The machine Dr. van de Graaff will begin building this week will handle 15,000,000 volts. On the bottom will be two sets of railroad tracks 14 ft. apart. On each track will be a four-wheel truck. On each of the two trucks will be a heavy iron casting, on which will stand an insulated paper cylinder 6 ft. in diameter, 28 ft. high. Inside each cylinder and at its bottom will be an electric motor. At the top of each cylinder will be a polished, hollow aluminum ball 15 ft. in diameter, weighing 2,600 Ib. From pulley wheels within each ball to the motor below stretch belts going 120 m. p. h. The swiftly moving belts are to pick up static electricity, deposit it on the balls--negative on one sphere, positive on the other. By such simple means Dr. van de Graaff expects to build up a negative potential of 7,500,000 volts on one sphere, a positive potential of 7,500,000 volts on the other. When the loaded spheres are trucked along the railroad tracks to within 15 ft. of each other, the resistance of the intervening air to their enormous stores of electricity breaks down: 7,500,000 volts crash against 7,500,000 volts. But when the machine is working it will not be permitted to waste its strength. Its crashes will occur within a huge x-ray tube which will extend 15 ft. from ball to ball For such a big contraption there must be a big house. President Compton found a proper shelter in the dirigible hangar at South Dartmouth, Mass, on the Round Hill estate of Col. Edward Howland Robinson Green, versatile and venerable son of the late famed Capitalist Hetty Green.

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