Serendipity, Scientific Discovery, and Project Cirrus Walter On Roberts Lecture Duncan C. Blanchard Albany, New York ABSTRACT Irving Langmuir defined serendipity as the art of profiting from unexpected occurrences. Numerous such occur- rences during World War II led Langmuir and Vincent Schaefer from research on gas masks through a variety of defense- related projects ending with the supercooling of clouds. Serendipity led Schaefer to discover that dry ice could nucleate ice formation in supercooled clouds and Bernard Vonnegut to discover ice nucleation by silver iodide. The government- sponsored Project Cirrus grew out of these discoveries. During Project Cirrus (1947-52), many serendipitous discover- ies and inventions were made, opening up areas of research still being pursued today. There has been speculation on why the role of serendipity is seldom mentioned in reporting discoveries in technical journals. The aversion to it may be ego related, the feeling that chance or luck is not good science. Editors inadvertently discourage it by the straight-jacket requirements in the writing of papers. By being curious, persevering, widely read, and aware that many branches of knowledge must often be brought to bear on a problem, one can be prepared to expe- rience serendipity when it occurs. l.On the mountain of Mount Washington in the winter, so it is likely that he had asked this question before, if only to him- On a cold winter's day early in 1946, three men self. But this time, with Schaefer, his long-time as- climbed slowly up the Lion's Head Trail that led to sistant at his side, an animated discussion took place. the summit of New Hampshire's Mount Washington. Though Schaefer, like Langmuir, had long been fa- From time to time they stopped to rest and speculate miliar with the supercooling of clouds, it is possible over some interesting and curious observations they had that Langmuir's question caused him to pose one of made as they approached the base of a supercooled his own. What could stratus cloud that hung like a veil around the upper part be done to hasten the of the mountain. Two of the men, Irving Langmuir process of the produc- and Vincent Schaefer, were staff scientists at the Re- tion of ice crystals, a search Laboratory of the General Electric (GE) Com- prerequisite for the pany in Schenectady, New York. The other, Raymond Bergeron (1935) pre- Falconer, a member of the Mount Washington Obser- cipitation mechanism vatory, had on many occasions climbed this trail to (which works because the top. Years later Falconer (1993) recalled that as the vapor pressure of they stood looking up at the stratus cloud deck supercooled water is Langmuir said, "Vincent, why, with all this heavy slightly higher than overcast, is there just one snowflake falling here and that of ice) to get another over there?" started? During the This was not the first time Langmuir, winner of the next several months 1932 Nobel Prize in chemistry, had climbed to the top Schaefer carried out numerous experiments. He devised an elegantly ©1996 American Meteorological Society simple piece Of appara- Duncan C. Blanchard 12 57 Bulletin of the American Meteorological Society Unauthenticated | Downloaded 10/08/21 07:21 PM UTC tus for producing and maintaining a supercooled cloud that a definition similar to Langmuir's is used by in the laboratory. This, the now-classic Schaefer cold many dictionaries today. box, was destined to usher in a new era in experimen- The idea behind serendipity, the art of profiting tal meteorology. from unexpected occurrences, is so important in dis- Though both Langmuir and Schaefer were avid covery that some eminent scientists have given their hikers and skiers and, in general, liked the open air in own views on how discoveries are made. Louis Pasteur, all kinds of weather, that was not the primary reason in an oft-quoted statement, said that, "In the field of they were climbing Mount Washington. They had observation, chance favors only the prepared mind." been doing experiments on the top of the mountain No mention of serendipity here, but Pasteur's chance on aircraft icing. How did these two men, who just 6 and prepared mind are analogous, respectively, to years before were deeply involved in fundamental Langmuir's unexpected occurrences and art. The research on surface chemistry, end up studying air- discoverer of vitamin C, Nobel Laureate Albert craft icing in the supercooled clouds that often blan- Szent-Gyorgyi, may not have had serendipity in mind keted the top of Mount Washington in the winter? It when he said that discoveries are made by those who, was because of serendipity. "see what everybody else has seen, but think what nobody else has thought." Few, however, would quar- rel that he, Langmuir, and Pasteur were saying essen- 2. Serendipity: The word tially the same thing. Langmuir—whose research spanned a wide spec- trum of science, from gas-filled lamps, submarine de- 3. From gas masks to aircraft icing tection devices, and theories of atomic structure to plasmas (he coined the word) and surface chemistry— The chain of unexpected events that led Langmuir was forever fond of saying it was serendipity that led and Schaefer to the supercooled clouds on Mount him from one subject to another. He believed so Washington had its beginning in 1940 when the U.S. strongly in the role of serendipity in scientific discov- government, concerned about the increasing number ery that he altered the dictionary definition of the word of German military victories in Europe and Africa, by defining serendipity as the art of profiting from un- began making preparations for possible entry into the expected occurrences (Langmuir 1948). war. Afraid that the Germans might use poisonous The word originated with Horace Walpole, a man smokes against combat troops, the National Defense of letters and connoisseur of the arts in eighteenth- Research Committee asked Langmuir to look into the century England. In 1754, in a letter to a friend, he development of a mask to filter out such smokes. wrote about an interesting discovery he had made Conventional gas masks would not work. They were about a painting, a discovery he had not been seek- designed to filter out gases, not the particles that com- ing. He said this was an example of serendipity. He pose smokes. Langmuir accepted the challenge. coined the word after remembering that, "I once read It is important to note that though Langmuir and a silly fairy tale called The Three Princes ofSerendip; Schaefer had many things in common, especially their as their highnesses traveled, they were always mak- love for research, the outdoors, and the continual ques- ing discoveries, by accident and sagacity, of things tioning of nature, it is hard to imagine two men of they were not in quest of" (Austin 1978). In more different backgrounds and training. Schaefer had Walpole's definition of serendipity, the discovery dropped out of high school to help his parents sup- must be both accidental and not sought, while port a large family. About the time Langmuir won his Langmuir's makes no distinction whether the discov- Nobel Prize, Schaefer was a machinist at the General ery had been sought for or not. To Langmuir, it was Electric Research Laboratory. His skill at designing only the accidental or unexpected occurrence that and building laboratory apparatus was recognized by mattered. Though it has been argued that a definition Langmuir, who brought him out of the machine shop of serendipity like Langmuir's should be called and into his lab. During the 1930s these two men pur- pseudoserendipity (Roberts 1989), I intend to make sued a variety of problems in surface chemistry. It was no distinction between the two in discussing the ex- an extraordinary scientific symbiosis in which the amples of serendipity that follow. The reader can older Langmuir would make theoretical predictions decide which is which. It should be noted, however, for their latest scientific puzzle, while the younger 1280 Vol. 77, No. 6, June 7 996 Unauthenticated | Downloaded 10/08/21 07:21 PM UTC Schaefer approached the answer with deceptively simple most of the time, immediately becomes covered with experiments. By letting both theory and experiment ice .. due to the presence of supercooled water drop- feed back into each other, they made rapid progress. lets. We had heard about rime, we had seen it, but we But before they could begin the development of did not know it occurred all the time at a place like smoke filters, they had to learn how to make smokes Mt. Washington. There are very few winter days with- with which to test the filters. Over many months out it. This puzzled us a lot." Langmuir theorized about the proper design of a filter, Langmuir and Schaefer eventually obtained some while Schaefer did the experiments. "That work lasted measurements on precipitation static, but the phenom- for about a year," said Langmuir (1948). "We obtained enon of supercooling kept haunting them. When fairly successful theoretical results and a better under- Langmuir found that the government was just as in- standing of how to build a good filter. But notice what terested in the problem of aircraft icing, here was an- we did incidentally; we acquired a great deal of detailed other "unexpected occurrence" that allowed him to knowledge as to how to make a smoke which would be leave the precipitation static problem and pursue one non-volatile, which would consist of very, very small related to supercooling. The two men measured the particles, far smaller than those of any ordinary smokes, rate at which icing built up on rotating cylinders of and we learned much about their optical properties." different sizes as they were being exposed to super- In the summer of 1941 there was an unexpected cooled clouds moving by at known speeds.