The Year Without Summer by William K. Klingaman, Nicholas P. Klingaman Page B

investigations helped Americans in their
     ceaseless pursuit of material wealth, so much the better.
    *   *   *
    I N the early nineteenth century, most meteorological instruments in the United States
     and Europe were owned by gentleman scientists, who collected data for their private
     diaries or to share with their colleagues in learned societies. Many of the rest of
     the instruments were located on ships: British Royal Navy vessels, for instance, were
     required to measure the air temperature, ocean temperature, wind speed and direction,
     and the fraction of the sky covered by cloud four times a day. (In a testament to
     British military discipline, navy logbooks reveal that ships continued to make regular
     readings even when taking enemy fire.) Barometers and thermometers were the most common
     instruments, having been developed over the previous 150 years. While some of the
     earliest models provided results of questionable accuracy, by 1816 the designs of
     both instruments had been refined so that they were able to provide precise and reliable
     measurements of the atmospheric pressure and temperature, respectively.
    Anemometers (for measuring wind speed) and hygrometers (for measuring humidity) were
     far less common and less accurate. There was no standard method for measuring wind
     speeds until Sir Francis Beaufort’s eponymous scale, developed in 1805, was adopted
     by the Royal Navy in the 1830s, and wind forces would not be related to anemometer
     measurements until the 1850s. It is nearly impossible to compare the readings from
     earlier anemometers, since the designs of the instruments and the scales applied to
     their measurements varied so widely. Most hygrometers of the early nineteenth century
     were simply the combination of two thermometers: one kept dry and the other immersed
     in water. As the water naturally evaporated, it cooled the wet thermometer; the temperature
     difference between the two thermometers could then be used to determine the humidity.
     In 1783, the Swiss physicist Horace-Bénédict de Saussure demonstrated the first hygrometer
     based on the contraction and expansion of human hair due to changes in atmospheric
     moisture. While his design would later become very popular, in 1816 it had not yet
     been widely adopted. (Currently, the most accurate hygrometers are polished mirrors
     that are cooled until water condenses onto them, an adaptation of a technique pioneered
     by the British chemist John Frederic Daniell in 1820.)
    Although barometers and thermometers were in widespread use throughout Europe and
     the United States throughout the eighteenth and into the nineteenth centuries, many
     weather diaries remained private; those records that have been published often contain
     long gaps or end abruptly. The meteorological community was primarily composed of
     amateurs, albeit enthusiastic ones, rather than professionals. Governments had not
     yet established official agencies with the responsibility for monitoring or understanding
     the weather—the Royal Meteorological Society in Britain, for example, was not founded
     until 1850—and, as during the French Revolution, those that did exist could be disbanded
     if they became politically unpopular. The information we have today about the climate
     of the period is the result of the painstaking, meticulous reconstitution by modern
     climatologists of fragmented data from disparate sources around the globe.
    Those nineteenth-century scientists who had access to instruments and kept detailed,
     regular records would have been aware of the connections between the variations in
     temperature and pressure and the variations in local weather patterns. Such variations
     had been noted for nearly two hundred years. Evangelista Torricelli, the Italian physicist
     and mathematician who invented the mercury barometer in 1643, soon recognized that
     the atmospheric pressure changed from one day to the next. Four years later, famed