On clear summer nights in 1908, visitors to Robert Wood鈥檚 Long Island farmstead were enchanted by the visions that appeared in the disused well house next to the barn. Gathered by the well after dark, they watched in astonishment as galaxies and star clusters floated above it. To keep himself amused, Wood had turned the well into a strange sort of telescope: for a mirror it had a pool of mercury rotating slowly at the bottom. News of this curious device spread fast, and before long, Wood was being offered impressive sums of money to build a much larger version. Its backers planned to use it to beam light signals to Mars in the hope of receiving a reply from the intelligent beings they assumed were living there.
TRANSFORMING an old well into a telescope with nothing but a spinning basin of mercury was just the sort of crowd-pleasing experiment that Robert Wood delighted in. As a child growing up in the suburbs of Boston, he amazed the neighbourhood kids by making water flow uphill by siphoning it out of a pond with a garden hose. Running the hose from the pond to lower ground nearby, he made sure to pass it over, rather than under, an intervening fence, for dramatic effect. 鈥淥ver the fence went the hose and all the water from the pond, until it was completely drained,鈥� recounted the Saturday Evening Post years later. 鈥淔riend and enemy gazed in awe at young Merlin.鈥�
Wood lost none of his playfulness as an adult. On his honeymoon in Yellowstone Park in 1892, he poured fluorescent dye into a geyser when no one was looking. A few minutes later, a group of tourists and their guide were startled by the eruption of a brilliant green fountain.
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In the summer of 1908, then, Wood could not have been ignorant of the potential for spectacle as he installed a basin full of mercury and a motor in the shaft of an old brick well on the farmstead that doubled as his summer home and laboratory. Yet even he could not have expected the stir he was about to make.
The concept was simple. Fill a basin with mercury and set it spinning, and the surface of the silvery liquid curves to make a parabolic mirror. This is just the right shape to focus light to make images in a telescope without the expense and labour of grinding and polishing a parabolic mirror from glass.
The idea of making a telescope mirror from a spinning basin of mercury had been around since at least 1850, when Italian astronomer Ernesto Capocci described the concept in a letter to Belgium鈥檚 Royal Academy of Sciences. In the late 1860s, English astronomer Richard Carrington experimented with a steam-powered version. Yet the liquid mirror had never come to anything, for one simple reason: images would be ruined by ripples on the surface of the mercury, not least those caused by the vibration of the motor that kept the mirror spinning.
Wood was not an astronomer but an experimental physicist and by 1901 a professor at Johns Hopkins University in Baltimore, Maryland. He had a knack for finding simple solutions to problems that defeated others and in 1908, as a diversion during the holiday, he set himself the challenge of making a practical mercury telescope. After experimenting with motors and magnets and small bowls of mercury, Wood settled for a 50-centimetre dish connected to a motor by fine rubber bands, which transmitted the required rotational force but not the motor鈥檚 vibrations.
Now to build a telescope. The old well house suited Wood鈥檚 purpose perfectly. With a hole cut in the roof, the building would be his observatory. He filled the well with lumps of rock and cement to just above the water level, creating a solid base, and then lined the walls with cement. The result was a watertight tube about 4 metres deep and 75 centimetres across. This was too tight a squeeze to work in so he had a second pit dug just outside the well house and a tunnel to link the two. Once he had installed the mercury mirror at the bottom of the well, all that remained was to start the motor.
By the time Wood set the mirror spinning it was well past dark, and he was at once rewarded with a view of the Milky Way鈥檚 ghostly glow as it passed overhead. 鈥淚ts appearance when I observed it from the roof of the house the first time the motor was started amply repaid me for all my trouble,鈥� he wrote a few months later in : 鈥淣o eyepiece was used, the star images appearing in space about 3 feet above the mouth of the pit鈥� rising and falling rhythmically, dancing up and down like will-o鈥�-the-wisps.鈥�
鈥淭he stars rose and fell rhythmically above the mouth of the pit鈥�
Light reflected from the mirror came to a focus above ground, giving the illusion that cosmic objects were floating over the well. Wood鈥檚 friends and neighbours were entranced, and soon the press was, too. By August, the device was headline news in The New York Times. Reports quickly spread around the world and the well 鈥渂ecame a shrine for pilgrimages of scientists and curiosity seekers鈥�. Even the director of the Harvard Observatory, Edward Pickering, couldn鈥檛 resist taking a peek.
Wood鈥檚 device had cost just $200, a modest sum even then, and there was much excitement about the possibility of scaling up the prototype to begin an era of cheap and enormous telescopes.
The next spring, Wood began to receive a flurry of telegrams from a group of astronomy enthusiasts in Texas. They were enthralled by the possibility, much discussed at the time, that intelligent life might exist on Mars, given the 鈥渃anals鈥� some said they could see on the planet鈥檚 surface through a telescope. They wanted to try to establish communication with the Martians, and reckoned they could do it by flashing light signals towards the Red Planet, using sunlight focused by a set of giant mercury mirrors. They promised to put $50,000 at Wood鈥檚 disposal to make their scheme a reality.
Beside his out-and-out pranks, Wood was not above proposing far-fetched schemes of his own. Even he considered the idea of signalling Mars with giant mercury mirrors wildly impractical, however. It would be much simpler and just as effective, he told The New York Times, to attract the attention of any Martians by creating a vast black spot on Earth with strips of dark cloth. By rolling up and unrolling the strips periodically, the spot would seem to wink, catching the eye of any alert Martian astronomer. 鈥淲e should probably get an answer, for the Martians are supposedly older and wiser than we are,鈥� Wood wrote.
By the end of that summer, Wood had abandoned the mercury telescope. He had rid it of the most crippling vibrations, though occasional annoyances remained. 鈥淭he approach of a horse and carriage could be detected鈥� when it was an eighth of a mile away,鈥� he explained in The Astrophysical Journal, 鈥渁nd the footsteps of a person running across the lawn 50 yards from the telescope house caused a perceptible vibration of the image鈥� and after every storm, vibrations were found resulting from the pounding of the surf on the beach a quarter of a mile distant.鈥�
Two much larger obstacles still stood in the way, however. Slight fluctuations in the running speed of the motor caused the position of the telescope鈥檚 focus to shift, which is why the images floated up and down 鈥渓ike will-o鈥�-the-wisps鈥�. Perhaps more importantly, the mercury telescope could not be tilted to point at different targets in the sky, limiting it to observing whatever celestial objects happened to pass directly overhead.
The idea lay dormant for more than 70 years. Then in the early 1980s, Ermanno Borra, an astronomer at Laval University in Quebec, Canada, picked up where Wood had left off. 鈥淲hen I looked at what Wood had done, I thought, my God, with the technology nowadays the problems he was running into are nothing,鈥� Borra says.
By the 1980s, steadier motors were widely available, easily eliminating the one serious source of distortion Wood had not solved. Just as important, since Wood鈥檚 time astronomers have learned how to glean useful information by surveying strips of sky, giving telescopes that are limited to staring at what passes overhead an important role.
Following positive results from several experimental liquid-mirror telescopes, a group of astronomers from Belgium and Canada, including Borra, is now preparing to build a high-altitude observatory with a 4-metre mercury mirror in the mountains of northern India. The International Liquid Mirror Telescope is expected to make its first observations in January 2010.