Free First Light: The Search for the Edge of the Universe by Richard Preston Page B

Carborundum grit. They used finer and finer grades of Carborundum and then switched to red jeweler’s rouge. By 1941, they had polished away five and a quarter tons of glass, had used up thirty-four tons of abrasives and jeweler’s rouge, and had brought the surface of the Pyrex disk down to a hollow sphere. From there they had to deepen the glass slightly into a paraboloid. A paraboloid is a saucer that focuses light to a point. The layer of glass that they had to remove in order to parabolize the mirror equaled the thickness of half a human hair. This work required eight more years of polishing, interrupted by World War II, when Caltech halted work on the telescope.
    The opticians were afraid that their machines would drop a metal filing on the glass. A grain of metal or grit trapped between the polishing tool and the glass would have cut a helical scratch in the glass that would have delayed the project for six months, or perhaps for years. They swept the room with vacuums and electromagnets. Then they looked at the dust they had collected under a microscope, classified the particles, and saved them in envelopes. If they saw a dust particle of a type they did not recognize, they stopped all their machines until they could trace the particle to its source. Toward the end of the polishing, the opticians spent more time testing the glass than rubbing it, fearful that they might polish too deeply in places, especially around the outer edge of the glass, in which case they might never be able to resurrect a true optical surface. Their testing apparatus was keen enough so that an optician could place his hand on the glass for a minute until the glass warmed, take his hand off it, and see a swelling in the shape of a hand persist on the glass. Before they looked at theglass through the testing apparatus, they had to turn off all fans and prevent people from walking around the room, “because a current of air coming through the room made the air look like a smoke screen,” Mel Johnson said. He remembered seeing waves twitching along the surface of the glass, as if the glass were restless, gently pulsing with life. The waves mystified the opticians, until they discovered that the mirror was picking up harmonic vibrations from traffic on California Boulevard, near the optical shop. After that the opticians scheduled precision testing of the glass for early Saturday mornings.
    When the surface of the glass had reached a fairly acceptable paraboloid, the opticians removed the plug from the hole in the center of the glass. In November 1947, they mounted the glass in a steel mirror cell (it would never leave the mirror cell again) and put it in a box and carried it in a flatbed truck up Palomar Mountain. The purpose of the superstructure of the telescope is to move the glass around and to keep it pointed at one spot in the sky. The purpose of the glass is merely to support five grams of reflective aluminum in a perfect paraboloid, in order to focus starlight into a camera. John Strong, a physicist, had invented a technique for depositing aluminum on glass. Strong had taught the Caltech opticians his trick and then moved on. He eventually wrote a textbook on physics. When I asked around Caltech about John Strong, people seemed to think that he was dead. I made some telephone calls to various parts of the United States and turned up John Strong in Amherst, Massachusetts, nowhere near dead, because he was working on a new edition of his textbook. “I never saw the mirror again,” Strong said over the telephone. He explained that he had had to clean the glass in order to make the aluminum atoms stick to it, for he had learned that oil from the human skin, which inevitably got on the glass from the opticians’ hands, caused aluminum to crinkle off. Strong had tried washing astronomical glass with chemical solvents, but no solvent seemed powerful enough to remove skin oil. Then Strong discovered Wildroot Cream for the hair. “I never