national academy of sciences cHarles Greeley aBBot 1872—1973 A Biographical Memoir by david H. devorkin Any opinions expressed in this memoir are those of the author(s) and do not necessarily reflect the views of the National Academy of Sciences. Biographical Memoir Copyright 1998 NatioNal aCademies press washiNgtoN d.C. h c a hr c a B y b h p a gr o ot h P CHARLES GREELEY ABBOT May 31, 1872—December 17, 1973 BY DAVID H. DEVORKIN C HARLES GREELEY ABBOT was the second director of the Smithsonian Astrophysical Observatory and the fifth Secretary of the Smithsonian Institution. He was the sec- ond and last person to hold both posts simultaneously and is remembered today for his skill as an instrumentalist and his unshakable belief that the Sun is a variable star and that its variations had a measurable effect on the Earth(cid:213)s weather. He was elected to the National Academy of Sci- ences in 1915 and served as its home secretary from 1919 to 1923 under President Charles Doolittle Walcott, who was Abbot(cid:213)s predecessor as Smithsonian Secretary. Abbot was born in May 1872 in Wilton, New Hamp- shire, the son and grandson of farmers. The youngest of four children of Harris and Caroline Ann (Greeley) Abbot, Charles Greeley attended public schools, but finished at Phillips Andover Academy. He then attended MIT, where he graduated in 1894 with a thesis in chemical physics. He expected to teach, but remained at MIT, studying osmotic pressure and earning an M.Sc. in 1895. Skilled at labora- tory work, he came to the attention of Samuel Pierpont Langley, who was looking for an assistant at the Smithsonian(cid:213)s Astrophysical Observatory (APO). Abbot soon was hired, though he lacked any experience in astronomy when he 3 4 BIOGRAPHICAL MEMOIRS arrived in Washington in June 1895. Langley, however, was not a traditional astronomer and Abbot was just the type of assistant he wanted to aid his mapping of the infrared spectrum of the Sun, adapting bolometers for photographic recording and determining dispersion standards for rock- salt and fluorite prisms to measure fundamental wavelengths in the infrared region of the solar spectrum. Under Langley, Abbot flourished as a creative designer and builder of delicate devices for measuring solar radia- tion. As Langley focussed more and more on his aeronau- tical experiments, Abbot, working with F. E. Fowle, be- came responsible for maintaining the observatory(cid:213)s solar program, including an expedition to observe the 1900 so- lar eclipse in Wadesboro, N.C., where Abbot applied a vastly improved bolometer to take readings of the Sun(cid:213)s inner corona. He was also a leading member of the Ameri- can eclipse expedition to Sumatra in 1901. He proved to be a reliable observer and impressed many astronomers who encountered him at these places. Abbot was an affable fellow, deferential to his superiors while making significant contributions to the mission of Langley(cid:213)s institution. That mission, very much representa- tive of the times, was to demonstrate the utility of govern- ment-supported science. Years later, in his rambling auto- biographical essay Adventures in the World of Science, Abbot recalled Langley(cid:213)s words explaining why measurement of the heat of the Sun was important: If the observation of the amount of heat the sun sends the earth is among the most important and difficult in astronomical physics, it may also be termed the fundamental problem of meteorology, nearly all whose phe- nomena would become predictable, if we knew both the original quantity and kind of this heat.1 Certainly the idea that solar radiation governed the Earth(cid:213)s fate as an abode for life was not original with Langley. The CHARLES GREELEY ABBOT 5 key to Langley(cid:213)s mission, however, was to make the amount and character of that radiation (cid:210)predictable(cid:211) and thereby useful for planning strategies for agricultural management and control. Langley believed that solar radiation varied in a cyclic manner. As Smithsonian Secretary, however, Lan- gley had other interests, but what may have been promo- tional rhetoric for him became a permanent and passion- ate conviction for his able, dutiful assistant. Within a few weeks of Langley(cid:213)s death in February 1906, Abbot was made acting director of the APO, becoming its second director in 1907 under Secretary Charles Walcott. Astrophysical operations continued unabated, with Walcott providing advice and support that allowed Abbot to ex- tend Langley(cid:213)s mission in two ways: first, by developing refined techniques for the specific determination of the solar constant; and second, by applying these techniques in a standardized manner to build a synoptic monitoring program that would search for solar variations. As under Langley, Abbot found Walcott wholly attuned to the pro- gressive notion of useful science. Before he became the Smithsonian(cid:213)s fourth Secretary, Walcott was head of the U.S. Geological Survey, and campaigned for practical research in publicly supported agencies. When Abbot became APO director in 1907, American astronomy(cid:213)s most significant strengths and potential lay in vast cataloguing projects centered at a few major observa- tories, including Harvard, Yerkes, and Lick. American as- tronomy was in the throes of organizing itself as a profes- sion, and its standards and modes of conduct were in flux. Celestial mechanics and mathematical astronomy were still the strengths of the discipline, but now the photographic plate and the spectroscope were available for assessing the physical nature of the Sun and stars. Langley had prac- ticed the new astronomy. Primarily an engineer, he had 6 BIOGRAPHICAL MEMOIRS created an astrophysical program at the Allegheny Observa- tory in Pittsburgh, defining it by the use of new types of instruments, the bolometer and spectrobolometer, and brought both these instruments and their practice to the Smithsonian to establish the first and only federally funded astrophysical observatory in the United States. When Abbot retired as APO director and as Smithsonian Secretary in 1944, setting a precedent as the first Smithsonian Secretary not to die in office, most but not all of the great cataloguing projects were gone and the discipline was un- dergoing profound change. Problem-oriented research, in- formed by modern physical theory, dominated the disci- pline. Yet the Smithsonian(cid:213)s Astrophysical Observatory pursued its single mission all along, elaborating on its purpose not by a broadening of its astronomical base but by refining its instrumentation and technique, searching for evidence that Earth(cid:213)s meteorology and biology were intimately connected to variations in the Sun(cid:213)s output of energy. Although he eschewed physical theory, Abbot was thoroughly modern in his problem-oriented approach to research. Thus, his failure to broaden the astrophysical scope of the APO during his long tenure has to be appre- ciated as due to a complex set of factors centered on his singular sense of mission, which transcended disciplinary lines between astronomy, geophysics, meteorology, and bi- ology. The amount and character of the Sun(cid:213)s radiation are basic quantities for a wide range of scientific and environ- mental concerns. Determining these quantities in practice, however, was far from simple. Astronomers long knew that the absorption of solar energy by the Earth(cid:213)s atmosphere was both selective and general. Langley(cid:213)s method of deter- mining the solar constant was to take observations of the Sun as it rose in the sky, noting its increase in radiating CHARLES GREELEY ABBOT 7 power and then extrapolating to the top of the atmosphere. Given the vagaries of the atmosphere and the limitations of technology, the value of the solar constant could vary as much as 50%. Langley established the value 3.00 cal/cm2/ min outside the atmosphere as the Smithsonian standard and held to it tenaciously to the end of his life. But others who made different assumptions about atmospheric ab- sorption coefficients or other variables came up with val- ues between 1.5 and 4.0. After some seven years working for Langley, Abbot knew that the Smithsonian value for the solar constant was too high, but he carefully avoided the issue until he was in charge. Then, he quickly announced results from observa- tions at Mount Wilson, California, that reduced the solar constant first to 2.1 and then to 1.93, largely through the introduction of improved, standardized methods and bet- ter thermal isolation for his pyrheliometers and bolom- eters.2 Abbot paid close attention to detail. Abbot(cid:213)s revision, however, drew criticism from various quarters, mainly from a disgruntled and generally combat- ive Langley protege, but also from two Europeans who argued that the way in which he accounted for atmospheric absorption was incorrect. Abbot met this criticism by re- turning to the highest mountain in the Rockies, following Langley(cid:213)s lead in 1881. Abbot cooperated with W. W. Campbell at the Lick Observatory and with the Sierra Club to build a sturdy field station on the summit of Mount Whitney. Abbot used the site sporadically in 1909 and 1910 to measure the solar constant and accompanied the Lick astronomers to study the spectrum of Mars. Still harried by critics, however, Abbot turned to balloonsondes to reach greater heights. Collaborating with the Weather Bureau and Signal Corps, with Anders Knut Angstrom, who had been in residence for several years, 8 BIOGRAPHICAL MEMOIRS and with the help of his chief assistant Loyal B. Aldrich, Abbot flew special pyrheliometers on balloons. He created a new type of robotic pyrheliometer out of parts from standard Weather Bureau meteorgraphs that was fully au- tomatic and self-recording. Automatic techniques for me- teorological observations from balloons were well devel- oped by then. But Abbot was the first to use such automata in America for astronomical measurements. Abbot(cid:213)s instruments, built by Andrew Kramer, were mar- vels of sophistication and planning. They were flown by Aldrich from the California coast in 1913 and 1914, and some of the balloonsondes reached over 25 kilometers; at least one of them returned clear evidence for thermomet- ric and barometric variations that confirmed his terres- trial extrapolations and allowed him to determine the value of the solar constant at the top of the Earth(cid:213)s atmosphere. This technical feat, requiring the cooperation of the Weather Bureau and the Signal Corps, quieted criticism of the Smithsonian value for the solar constant. It helped to af- firm Abbot(cid:213)s reputation and established the modern range for the solar constant. Even before he assumed the directorship of the APO, Abbot was among the astronomical elite. In a 1903 census by the AAAS he was listed among the top thirty astrono- mers by his peers. Langley was among the first rank, and both scored even higher among physicists who were polled. Abbot won the prestigious Draper Gold Medal of the Na- tional Academy of Sciences in 1910 and the Rumford Medal of the American Academy of Arts and Sciences in 1916. With his solar-constant critics vanquished, Abbot focussed more on Langley(cid:213)s ultimate goal: to search for evidence of variations in the solar constant and to show that these cycles influenced cycles in weather and climate. He be- lieved that such evidence was already at hand from the CHARLES GREELEY ABBOT 9 findings of H. H. Clayton, the chief forecaster of Argentina and a colleague of A. Lawrence Rotch of the Blue Hill Me- teorological Observatory outside Boston. Clayton had ex- citedly written Abbot in 1912 with what he believed was proof that changes in the world(cid:213)s weather correlated with changes in the solar constant that he had gleaned from published Smithsonian data. Clayton soon became one of Abbot(cid:213)s closest allies, and over the next three decades, confirming these clues would define Abbot(cid:213)s mission. To confirm Clayton(cid:213)s findings Abbot had to account for local variations due to seasonal weather conditions, and so he set about searching for widely spaced observing sites where air transparency was constant. High mountains in desert regions spread over the accessible parts of the Earth became his target, and again, following a well-worn Smithsonian tradition, Abbot built these stations in the manner of field expeditions. His first major permanent station was at George Ellery Hale(cid:213)s Mount Wilson Solar Observatory, which Abbot started visiting as it was being built in 1903 and 1904. Hale tried once to hire Abbot away from Langley, but soon accepted the Smithsonian man as an ally in Washington, where his own patron the Carnegie Institution of Washington was based. By 1915 Abbot had built a permanent field station on the south side of a spur of the mountain that emulated Hale(cid:213)s own tower telescopes. Abbot visited the station of- ten and built a large solar cooker which his wife Lillian used to bake and roast to feed the local staff. The Smithsonian was a welcome neighbor on that mile-high mountain top. With Walcott(cid:213)s backing, which included securing endorse- ments from astronomers around the world, Abbot soon gained additional funds to search for other sites to comple- ment Mount Wilson. In 1911 and 1912 he and Angstrom 10 BIOGRAPHICAL MEMOIRS set up a temporary station at Bassour in Algeria, where they observed the Sun and weather patterns using a wide array of sensors ranging from small portable pyrheliometers to Abbot(cid:213)s huge spectrobolometer, which sifted the Sun(cid:213)s ra- diation through a slowly rotating prism that focussed differ- ent parts of its spectrum onto a tiny platinum wire. The wire(cid:213)s electrical resistance was changed by the Sun(cid:213)s light heating it, and this caused a flow of current in a delicate galvanometer, which moved a tiny mirror supported by a quartz fiber. The moving mirror sent a beam of sunlight onto a strip of moving photographic film, which recorded the varying energy of the Sun as a function of wavelength. Throughout World War I Abbot maintained the Mount Wilson station and hoped to establish a southern hemi- sphere site too. He also attended to various wartime activi- ties. He patented a new way to rifle a bullet to improve accuracy and with Aldrich developed a portable search- light, making great friends with General Electric in the process. Abbot also promoted Robert Goddard and pushed Army Ordnance to award the Smithsonian a lucrative con- tract for Goddard(cid:213)s continued work on solid rockets. But after the Armistice, Ordnance canceled the contract, to Abbot(cid:213)s great annoyance. At the end of the war, Abbot reactivated his site search, looking for a place that would have clear weather during the poorer winter season in California. The new (cid:210)place(cid:211) had to be clear (weather) when his California site experi- enced cloudy weather. He had hoped to gain the coopera- tion of the Australian government, but eventually Wolcott approved the use of Hodgkins Fund income to build a sta- tion in South America, where the United States was build- ing a strong mining base. The Guggenheims operated a huge copper mine at Chuquicamata, and were happy to host a U.S. government presence. The mining company