| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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feature Surveyor of the Western Sky:
March 1, 1869. Fifteen members of the California Academy of Sciences are meeting on an upper floor of a Clay Street office building. Albert Kellogg is passing around pieces of meat collected near San Jose. According to reports, the meat had fallen from a cloudless sky across a twenty-acre area. A debate ensues about whether or not a windstorm could be responsible. This may seem like an odd way to spend an evening. For intellectuals, however, San Francisco in 1869 was severely lacking in civilized discourse. The Academy, then located in two small rooms in what would become San Francisco’s Financial District, was similar to the scholarly societies back on the East Coast. Among the participants were doctors, lawyers, clergymen—and a new member, George Davidson. As Chief of the U.S. Coast and Geodetic Survey’s Pacific operations, Davidson was one of few in the room with formal scientific training. At the Academy’s next meeting, the mystery of the raining meat was solved. Vultures stuffing themselves on dead cattle had disgorged some of their meal to stay airborne. More significantly, Davidson gave the first of many scientific talks to the members of the Academy. Davidson blew into the cozy group of gentlemen naturalists like a gale off the Pacific. He was elected President in 1872 and immediately began work to move the Academy to a larger space, open exhibits, hold public meetings, host noted scientists from around the globe, and collect funds to build a brand new museum. Under his leadership, the Academy would become a major force in the development and especially the popularization of astronomy on the West Coast. By 1879, in a quiet park perched at the edge of Pacific Heights, Davison had built an octagonal wooden structure and topped it with a rounded canvas tent. Inside, he mounted a telescope and spent his nights high above the city’s hustle, gazing at the heavens. He furnished the Lafayette Park observatory with a fine brass telescope, made by legendary instrument maker and optician Alvan Clark. The 6.4-inch, $5,000 refracting telescope already had a distinguished pedigree; appearing at the 1876 Centennial Exhibition in Philadelphia alongside such curious new inventions as the telephone, it won a gold medal. Trained as a surveyor, Davidson used his telescope to take precise measurements of the sky. He timed the moons of Jupiter as they orbited their planet, observed our Moon’s passage in front of distant stars, and carefully recorded the appearance of Saturn’s rings. Though Davidson made no astronomical discoveries of note, his meticulous observations helped motivate others and began California’s impressive astronomical tradition. Today, California is home to some of the finest astronomical instruments in existence. These white-capped domes pop from their respective hillsides like giant mushrooms, rumbling open at sundown to garner the secrets of the heavens. Mount Palomar, near San Diego, once housed the largest telescope on Earth. Edwin Hubble measured the age of the universe at Mount Wilson above Los Angeles. Astronomers on Mount Hamilton outside of San Jose bounced lasers off mirrors placed on the Moon by Neil Armstrong and Buzz Aldrin. But all of these came much later. Davidson’s small canvas dome was the granddaddy of them all, the first astronomical observatory on the West Coast. At public meetings of the Academy, Davidson would describe the wonders glimpsed through the eyepiece of his telescope: “The evening was clear and pleasant and nearly calm, and the smoke of the city was to the southeastward. With a moderate power of 120 diameters, the Cassini division of the ring of Saturn was visible all around, and the gauzy or dusky innermost ring was made out.” Davidson came from humble beginnings. His father, an English lacemaker, immigrated to the United States in 1832 with his wife and eight children. His mother, whom he described as having “great force of character,” homeschooled the children. She taught her son the scientific principles of the industrial age, demonstrating steam power and the mechanics of simple machines. After the family settled in Philadelphia, George gained entrance to its prestigious Central High School in the early 1840s. There he met Alexander Dallas Bache, an educator who had studied physics, astronomy, and geodesy, the measurement of the Earth. Young George took an almost immediate interest in Bache’s instruction, and began working at the school’s new observatory. There, he learned the basic principles of astronomy and how they related to the mapping of the Earth. By the time Davidson graduated, Bache had been appointed Superintendent of the United States Coast Survey. The future founder of the National Academy of Sciences immediately hired the young Davidson to map the coast of New England. When Davidson arrived in San Francisco in 1850, he had already helped survey the coastline of New England, the California/Nevada border, the Alaskan coastline, and Panama. In 1900, Davidson wrote that in the course of his work, he had traveled 401,888 miles—roughly sixteen times the circumference of the world. His surveying equipment included two special telescopes designed to pinpoint the observer’s latitude by measuring the angle of the North Star from the horizon. Longitude was more difficult to determine. Precise observations of the moon’s transits had to be timed and compared with charts of the projections. Davidson not only perfected these positioning techniques but also designed an improved transit telescope for determining longitude. This precise surveying work catalyzed in him a great and enduring interest in astronomy. At the Academy, Davidson assiduously courted local philanthropists to fund his ambitious projects. Of these, perhaps the wealthiest was San Francisco millionaire James Lick. Lick had made his first fortune selling pianos to the successful citizens of Lima, Peru. Arriving in San Francisco in January of 1848, Lick immediately invested $30,000 in 37 plots of land. At the time, San Francisco consisted of little more than a naval outpost, Mission Dolores, and a few cows. When the Gold Rush began just a few months later, San Francisco’s real estate values skyrocketed along with the local population. Lick’s real estate investments made him a millionaire three times over. A disagreement with his son over a pet parrot had left Lick with no direct heir and a lot of money to give away. Now Lick wanted a worthy monument to his name. His original decision to build a pyramid on Main Street “higher than those of the Egyptians,” was scuttled by fears that such an eye-catching structure would be targeted should San Francisco ever come under attack. Davidson’s visit turned Lick’s thoughts skyward. Nearly 80 and bedridden in a San Francisco hotel, Lick was fascinated by talk of Jupiter’s many satellites, the mountains on Earth’s Moon, and Saturn’s rings. An entry in the Academy’s Proceedings at the time read: “The dusky ring, where it crosses the body of the planet, does not present a uniform tone of color, but the inner circumference seems a little denser and darker than further out. This might arise from a narrow dark belt on the body of the planet just on the line of projection of the inner circumference on the body of the planet.” Such phrases would hardly woo a rich donor today, but Lick was enthralled. He requested a small telescope of his own to use through the hotel window and joined with Davidson to plan an observatory with a telescope “superior to and more powerful than any telescope yet made.” A telescope’s power comes from the amount of light it can collect. More light illuminates more details. Today’s large telescopes use mirrors to collect light. The mirror focuses the light onto a smaller mirror, which then bounces it to an eyepiece or, more commonly, an electronic detector. Such “reflecting” telescopes are nothing new; Newton figured out how to build one in 1668. At the turn of the last century, however, most major telescopes were “refractors.” This is the most common type of telescope: a long tube with a lens at one end that collects light and focuses it to an eyepiece at the other end. Refracting telescopes are more stable than reflectors, and are better suited for the kinds of precise measurements most astronomers were interested in at the end of the nineteenth century. The problem with refractors is that the tube in a really large telescope is hard-pressed to support the heavy chunk of lens glass needed to fit the aperture. When designing their telescope, Lick and Davidson decided on a lens 36 inches in diameter to be precision ground by Alvan Clark. Today it remains the second largest refractor telescope in the world. Next came the choice of a location for the greatest telescope in the world. Lick favored a site adjacent to the Academy of Sciences at 4th and Market Streets in downtown San Francisco. Davidson disagreed, holding firmly to the idea that the thin atmosphere of higher elevations would give more accurate views of the heavens. San Francisco, according to Davidson, was “unique for general unsteadiness of the atmosphere,” not to mention the added problems of city lights and smoke. Shifting air currents distort light, which is why stars seem to twinkle. Observing stars from beneath Earth’s atmosphere has been likened to observing a streetlamp from the bottom of a swimming pool. Davidson finally convinced Lick to locate the observatory at a high elevation to minimize this effect. At an Academy meeting in October of 1873, Davidson triumphantly announced Lick’s donation of $1.2 million towards a telescope to be located in the High Sierra, and then promptly left for Japan to observe a rare transit of Venus across the face of the Sun. With Davidson safely out of town, other groups hoping to benefit from Lick’s wealth mounted their attacks. An opposing faction within the California Academy of Sciences, as well as petitioners from the Society of California Pioneers, persuaded Lick that it would be foolish to give so much money to a telescope that no one would ever see. Davidson returned from his trip to find that Lick had not only chopped his original bequest nearly in half, but had relocated the observatory site to Mount Hamilton, on the edge of present-day Silicon Valley. Angered by the change in plans, Davidson abandoned the project. Lick did not live to see his telescope completed; he died in 1876, twelve years before Lick Observatory opened its doors. At the suggestion that his ashes be scattered at the observatory site, Lick replied, “No sir, I intend to rot like a gentleman.” Instead, he was buried in a sarcophagus at the base of Lick Observatory. Though Davidson’s wish for a truly high-elevation observatory didn’t come true, Lick Observatory was the first permanent mountaintop observatory in the world. It set the standard for nearly every major astronomical facility built since. Astronomers at Lick Observatory have become experts in the art of dodging Earth’s shifty atmosphere, skills which would surely mollify Davidson’s spirit. A laser is shot into the sky alongside the telescope, creating a glowing spot in the atmosphere. Astronomers observe how much this artificial star’s position shifts due to air currents. They use the information to push and pull on a small elastic mirror, finely adjusting its shape. When incoming light from real stars is bounced off this deformable mirror, it is corrected for atmospheric distortion. Under the right conditions, this adaptive optics system can produce clearer images than the Hubble Space Telescope at a fraction of the cost. Davidson also persuaded wealthy East Bay resident Anthony Chabot to build Oakland’s Chabot Observatory. The telescopes Chabot purchased are still in use at the Chabot Space Science Center, and remain among the best available for public use in the United States. Meanwhile, Davidson continued to conduct his own observations at Lafayette Park. In 1882, he took the telescope to Cerro Roblero, New Mexico, to witness the second in a pair of Venus-transits. In a transit, the tiny, black speck of a planet moves slowly across the vast disk of the Sun. For at least two hundred years, transits of Venus were considered to be one of astronomy’s main events. Timing such transits from different locations on Earth allowed astronomers to measure the distance between the Earth and Venus, and thus assign a scale to the solar system. Astronomers were sure that simultaneous observations of the second transit would teach them more about the planet itself. Observers noticed that Venus did not have a crisp edge as it slipped out from in front of the Sun’s disk. Rather, as Davidson noted, it had a “fine, white, faint, crescent of coronal light apparently surrounding part of the disk of Venus as an illuminated atmosphere.” Well aware that air currents can distort light, Davidson believed these strange observations were due to Earth’s own atmosphere, not the one around Venus. He accused astronomers of jumping to conclusions, seeking “explanations in some obscure cause or causes—such as the poor character of the objective used, the lack of sharpness in the limbs of the planets (owing to their possessing an atmosphere).” Unusually for him, Davidson was dead wrong. Venus does have an atmosphere, one far denser than our own, that almost certainly affects how Venus appears during a transit. Davidson described the transit of Venus at the Academy in 1897, his last year as President. Just three years later, his eyesight failing, Davidson stopped observing altogether. After the earthquake and fire of April 16, 1906, he opened the observatory to house women and children forced from their ruined homes. Fearful that the instrument would be damaged by aftershocks, Davidson had the telescope dismantled and stored in his house at 2221 Washington Street. After Davidson’s death in 1911, it languished in the dark for another 50 years. In 1945, Davidson’s little 6.4-inch Clark refractor came to the Chabot Observatory. It was finally called into action again in 1954, for a California Academy of Sciences expedition to Sweden to view a total solar eclipse. The very next year, it was used to help select the site for the National Astronomical Observatory that would eventually be built on Kitt Peak in Arizona. Today, the telescope resides at the Academy’s Hume Observatory in Sonoma County, where its views of the heavens continue to inspire whole new generations of astronomers. Kirsten Vanstone, a former staff member at the Morrison Planetarium, is an astronomer, educator, and armchair science historian. She now lives in Toronto, Canada. |
