Pouring Day

Before dawn one day last week workmen scurried about a dim, vast room in the Corning Glass Works at Corning. N. Y. For one day they were to be both stagehands and actors. For weeks they had rehearsed every movement they were to make during one eleven-hour performance--the pouring of the 2OO-inch (16 ft. 8 in.) telescope mirror for California Institute of Technology. High as a house in the centre of the room stood a furnace which had been under fire for three weeks. In its great belly was a 34-ton lake of molten pyrex borosilicate glass, white hot at 1.500DEG C. Three doors in its flank opened for ladles. Nearby was the mold--a circular tank 2 ft. deep, 17 ft. across, composed of insulated silicate brick, its floor studded with circular and triangular bosses laid out in a honeycomb design. Heated to 1,000DEG C., the mold was topped by a beehive-shaped, three-doored covering. At 8 a. m. outside the plant a crowd of 4,000 had gathered. At 8:30 on the pouring floor quiet, pious Dr. George Vest McCauley, the company's physicist in charge of operations, and genial Dr. John C. Hostetter, director of research, saw that everything was ready. In the deafening roar of gas blowers in the furnace and ventilating blowers cooling the factory Dr. McCauley could not make himself heard. He signaled his orders with his arm. A workman sprang to a windlass operating one of the furnace doors. Eight others manned the 20-ft. handle of a big ladle, hanging from an overhead monorail. By clenching a peg between his teeth, the '"front" man kept in place a rectangular face-shield. Above the din the carrier truck screeched on the overhead rail as the ladle was trundled up to the furnace. The door swung open to a blinding glare from the inferno inside. The ladle went in. came out full to the brim with a dazzling cargo which dripped down the sides in streamers and sheets. These were trimmed off by a furnaceman with a long hook as the ladlemen walked the dipper over to the mold, popped it through a door in the beehive, poured in 400 Ib. of glass turning from gold to silver as it cooled.

Hour after hour like a well-drilled football team the ladlemen dipped and poured load after load. The completed mirror was to weigh 20 tons: that meant 100 trips. To a balcony commanding the scene 50 spectators at a time were admitted, quickly shooed away to make room for 50 more. Mingling with newshawks on three platforms and watching at their leisure were some twoscore scientific notables: Sir William Bragg, Nobel prizeman now lecturing at Cornell; Mt. Wilson Observatory's famed Walter Sydney Adams; Research Directors Frank Baldwin Jewett of Bell Telephone Laboratories and Charles Edward Kenneth Mees of Eastman Kodak; Astronomers Otto Struve of Yerkes Observatory and Clyde Fisher of Manhattan; Assistant Director Lyman James Briggs of the U. S. Bureau of Standards and Dr. Arthur Louis Day, Carnegie Institution geophysicist.

A supervisor peered into the beehive, gave an alarm signal. Some of the mounds on the mold floor had worked loose, were floating on the surface of the glass. The iron bolts holding them in place had melted.

This was almost a disaster. Blacksmiths quickly improvised ten-foot tweezers with which the loose mounds were fished out. The pouring was resumed, with the prospect that when grinding begins on the big disk special hollows and grooves will have to be made in its back at the points where the mounds worked loose. Darkness had settled outside the plant when the last trip from furnace to mold was made.

It is six years since a 200-in. mirror, twice the diameter of the world's largest telescope mirror in use at Mt. Wilson, began to seem possible as the result of the Rockefeller Foundation's $6.000,000 grant to Caltech. Dozens of astronomers and industrial researchers have helped overcome the problems involved. Four more years lie ahead. In an annealing oven the disk will be cooled a few degrees a day until after about ten months it has reached room temperature. Then, if it can pass optical tests, it will be shipped to Caltech's laboratories in Pasadena. When three years of grinding (done slowly to avoid distortion caused by frictional heat) and cleaning with blasts of electrons have produced a concave paraboloid surface true to within two millionths of an inch, the mirror will be sprayed with vaporized aluminum. Some time in 1938. if all goes well, it will be mounted on great steel lingers fitted into its grooved back at the bottom of a 60-ft. skeleton steel tube in an observatory which Caltech astronomers will operate in conjunction with the Mt. Wilson staff. Not until then will astronomers look three times farther into space than they can see now.

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