The Perfect Machine (33 page)

Corning had done little ladling, and whatever experience they had, years before, was long before the development of Pyrex. To duplicate the process of filling a large mold, McCauley had Wally Woods try filling the molds with a small ladle, pouring half the contents of the ladle
into the mold and the balance into a cullet can, where cooled glass was collected for later reuse. When Woods took two or more pours to fill the mold, strata would appear in the glass. McCauley suspected that the glass on the surface of the tank, exposed to the air, was devitrifying. When Woods rotated the ladle in the tank to fill it, the surface glass of the tank would end up in the ladle, and ultimately on the top of the molded glass, producing a layer cake with devitrified frosting. The devitrified Pyrex not only marred the appearance of the glass but introduced strains that would degrade the optical performance of a mirror. It wasn’t good enough for a telescope.

The answer was to skim the surface glass off the ladle before pouring the balance of the glass into the mold. Woods explained that glass has to be skimmed with a paddle rather than a spoon. He fashioned the device he needed from a blow iron, and when he skimmed the surface off each ladle of glass before pouring it into the mold, the castings emerged with no strata. McCauley went home smiling that evening. He was ready to cast telescope disks.

Molding a large mass of glass is the first step of a complex process that physicists like McCauley were just beginning to understand. Large castings of glass are subject to strains that develop in the internal structure of the material as the mass of molten glass cools. The strains can be relieved, or sometimes eliminated, by annealing the glass—heating the mass of molten glass until it is free of strains, then gradually cooling the mass according to a precise schedule determined by the chemistry of the glass and the size of the mass being annealed. The larger the glass casting and the more critical the use, the more precise the annealing schedule must be. The process is demanding: If the cooling schedule is wrong, or if a failure of equipment drops the temperature too quickly, the casting will emerge with strains that show up as distortions, weaknesses, or instabilities. The mirror would be the largest piece of glass ever cast, and the optical demands put on the primary mirror of the two-hundred-inch telescope would be the toughest criteria ever applied to a large piece of glass. The annealing was crucial.

After the meetings in New York, McCauley asked two engineers, Howard Lillie at the Corning Laboratory and George Morey at the Geophysical Laboratory of the Carnegie Institution in Washington, to experimentally determine the annealing properties of the 702 Pyrex. The figures they produced for the annealing constant were inconsistent, but the required temperatures were high enough that McCauley knew he would need robust ovens, fine control of the temperature, and lots of power. It was theoretically possible to build a gas-fired annealing oven, but the fine temperature control he needed demanded an electrical oven.

Thanks to the many inventions of Edison and Thomson, and to General Electric’s production of high-tension transformers and power distribution switches, electrical grids were bringing the miracle of electricity
to vast rural areas of the United States in the 1930s. Factories switched over to electrical power even before homes. Electric motors allowed machinery to be portable, instead of requiring overhead belt drives that distributed the power from a central shaft driven by a steam engine or waterwheel. But even as electric power became ubiquitous, it was far less reliable than we have come to expect today. Generators and power lines failed regularly, lightning took out entire networks, and switching equipment and transformers fatigued or shorted out. For most usages, in an era before electronics, long-term reliability wasn’t a critical issue. But for the heating elements and controls in an annealing oven that might have to run for a year or more, reliability was the main concern. It was the one area of the project in which McCauley assumed that GE’s own work would prove useful.

In mid-November 1931, McCauley and his boss, J. C. Hostetter, went up to the GE laboratories in Lynn, armed with a letter of introduction from Gerard Swope. Ellis was friendly and accommodating. GE, Ellis assured them, could have built the disks of fused silica, and would have, if the new experiments with the one-hundred-inch telescope hadn’t eliminated the need for quartz disks. He knew about the prices Corning had quoted on the series of disks and openly contrasted the numbers with GE’s figure for a two-hundred-inch disk, somewhere between $750,000 and $1 million. When Hostetter pointed out that Corning had held discussions with the Observatory Council but didn’t yet have a firm order for the disks, Ellis assured him that he had inside information on the project and that the order was as good as placed.

Elihu Thomson showed up at the lab, greeted the two men from Corning, and wished them well. He left after a few minutes, and Ellis talked freely about the professor’s bitterness and disappointment that GE had been forced to abandon the project before producing a big disk. He proudly showed off the two sixty-inch disks the GE effort had produced—one good clear quartz, but split radially; the other filled with bubbles—and described his project to split the cracked disk and fuse the two halves together so it could be used for a solar telescope or other critical use.
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Much of the equipment in the GE laboratory had been paid for by and was therefore the property of the Observatory Council, but after surveying the huge building and facilities GE had created, McCauley concluded that the only useful equipment for Corning was some large transformers, pyrometric devices for measuring high temperatures, and a large crane. Ellis said that he would be using some of the equipment to finish his work with the sixty-inch disks, so the only transfer arranged was for three large transformers that GE had never used. Those, and the information that GE used a special industrial grade of nichrome as heating elements for furnaces, were McCauley’s inheritance from the years of work and hundreds of thousands of dollars GE had expended on the project.

McCauley wasn’t a man to criticize openly someone else’s work or plans, but he hadn’t been impressed with what he saw in Lynn. The fiendishly complex apparatus and the yard full of quartz chunks, waiting to be sorted underwater by one man, seemed like parts of a process doomed to endless experimentation and cost overruns.

His own plan was conservative. Although they would be working with a glass mixture that had never been used for large castings, the procedure of filling a mold with ladles was tried and true. Glassmakers had practiced those skills, with glass formulations simpler than Pyrex, for centuries.

McCauley had considered and rejected two alternate techniques. One idea was to “sag” the glass into the mold, by placing a large block of pure glass over the mold and heating it until it flowed into the shape of the mold. It was an appealing idea because it eliminated the process of ladling, but for the ribbed disks that the Observatory Council wanted, McCauley would need a mold with cores on the bottom strong enough to support the weight of the entire block of glass. No one had experience building that sort of mold out of refractory brick, the only material that could withstand the heat of molten glass. The alternative was to sag a disk of glass large enough to cover the entire mold. That meant they would first have to cast the unribbed disk, which would entail the costs and risks of two moldings and the risk of handling heavy materials twice.

Still, the sagging idea was promising enough to merit at least an experiment. One of the Corning melting tanks was scheduled to be shut down for repairs. Normally they would shut off the burners, letting the melt inside cool rapidly. The resultant cracks and strains would then leave a mix of small chunks of glass. Instead McCauley had insulation installed on the sides of the tank before the shutdown, and he slowly reduced the heat in the tank. When the tank was cool, large blocks of cullet were left behind. None was big enough for a two-hundred-inch telescope disk, but several were large enough to suggest that sagging chunks of pure glass was a possible alternative to ladling.

Another physicist at Corning, Dr. George Littleton, was famed for out-of-the-ordinary ideas. When he saw the plans for ribbed disks, he went back to his lab, muddled over a scratch pad, then suggested an alternative that he was convinced would be cheaper to fabricate, lighter, and substantially more rigid than a cast mirror. Instead of pouring glass into a shaped mold, Littleton proposed, they could start with Pyrex-brand custard cups, which Corning produced in immense quantities. The cups would be stacked inverted in layers in an open mold, which would then be filled with molten glass. The glass would flow around the cups and seal them into a single structure of regularly arranged thin glass walls enclosing a geometric pattern of air spaces. Littleton’s calculations demonstrated that the resulting honeycomb structure would be light and rigid, and the fabrication procedure avoided the complexities of building molds in complex geometric designs.

Making a telescope mirror from standard Pyrex custard cups was too audacious not to try. McCauley brought in a supply of the cups and put the mold makers and then Woods to work. When Woods ladled the molten glass into the mold, it flowed into the gaps between the inverted custard cups, sealing off air cavities here and there in the pile. As more glass was added, the pockets of trapped air, expanding with the increasing temperature in the mold, formed odd-shaped bubbles, turning the neat geometric pattern into chaos. McCauley and Littleton, each with a Ph.D. in physics, had temporarily forgotten that hot air expands.

The custard-cup experiment settled the method of making disks. McCauley would stick with his original conservative plan. He had the Corning purchasing department order large ladles, capable of holding three hundred pounds of glass, and told the foremen in the Corning factories to be on the lookout for experienced ladlers among their glassmakers.

McCauley had been impressed with the heavy-duty nichrome heaters he had seen at Lynn and the big transformers that GE had transferred to Corning. Willing salesmen had plied him with specification sheets for electrical control equipment. No order was too small to ignore in the depression. He was especially impressed with the large theater dimmers Westinghouse manufactured. The controls were simple, ruggedly built, and fitted with calibrated dials that could be rearranged as a vernier scale, which would allow precise adjustment of the temperature in the annealing oven. For safety he had the GE transformers rebuilt so they would take 2,200 volts from the main feeder lines coming into the Corning factory and put out a nonlethal 35 volts to the heating elements instead of the stock 110 volts.

McCauley drew up sketches for an annealing oven and turned them over to George Ward, an engineer who had worked on furnace
designs. Ward produced drawings and material lists for the Corning masons, millwrights, and electricians. The first oven, big enough to handle a thirty-six-inch disk, would be used to anneal the twenty-six-inch solid disk and a thirty-inch ribbed disk, the first ones on the schedule for the Observatory Council.

By March 1932 everything was ready except the annealing oven. George Crown, the favorite Corning mason for lab work, had built molds for the first two disks, shaping the nineteen separate cores that would create the ribbed structure from the reliable C-25 insulating brick, and cementing them to the molds with the Hi-Tempite cement that had been used on earlier molds. Although the annealing oven wasn’t ready, McCauley decided to go ahead by casting the disks, then cooling the blanks slowly under a layer of Sil-o-Cel powder insulation spread over the exterior of the hot molds. The cold disks could later be reheated and annealed when the ovens were ready.

Except for some bouts of stage fright among the ladlers, the first production casting, of the twenty-six-inch solid disk, went well. The first try at a ribbed disk was less successful. When Woods and his helpers ladled glass into the mold, small bubbles appeared in the spaces between the cores, and the cores slowly loosened and bobbed to the surface of the mold. Tests had showed that the cores should stay in place, but there was no denying the evidence. That evening McCauley went back to his drafting board at the oak dining table where Anne, Jim, and George Jr. did their homework.

For the next try McCauley had the mold makers use cemented dowels to hold the cores in the mold. The crew was reassembled at four A.M. on a Sunday, so there would be no curious audience of glass-workers to make the still-inexperienced ladlers nervous. They were alone except for a cleaning crew working in the steel girders and trusses of the roof, oblivious to the critical work on the floor beneath them. Dust and debris tumbled down into the open mold. Shouting and sign language finally routed the cleaning crew to another area of the building; a worker used a jet of compressed air to blow the debris out of the mold; and the ladlers started up again.

This time the cores held in place, but a cascade of bubbles rose from the surfaces of the mold, spoiling the disk. McCauley asked the mold makers and the men who had filled the tank to make sure that all materials in the mold and the batch of glass were exactly the same as they had used in the successful practice pours. An expert on gas analysis from the Corning labs punctured one of the larger bubbles in the disk and collected a sample. His gas spectrometer reported that the gas was from the combustion of a petroleum product.

For McCauley problem solving was a Sherlock Holmes game. He talked each member of the crew through the procedures they had used in the trial molds and the most recent efforts. Where had they gotten the bricks? Which cement had they used for the molds? Which lots
had the material for the glass melt come from? The only change he found was that the early molds had been cleaned with a vacuum cleaner. The technicians couldn’t get the nozzle of the vacuum cleaner between the cores that had been glued in place for the ribbed disk, so they had used compressed air to blow the mold clean.