Book review: The Man behind Degree Celsius : A Pioneer in Investigatingthe Earth and its Changes

The Man behind “Degree Celsius”: A Pioneer in Investigating the Earth and its Changes by Martin Ekman is a gem of a little book. It effectively describes not only the scientific discoveries and contributions of Anders Celsius after whom the temperature scale is named, but also how science was conducted in Sweden 300 years ago, the oversized impact of the little university town of Uppsala and its university founded in 1477, and the critical importance of making careful geophysical observations in space and time in advancing knowledge about our Earth. The book starts, not in the year 1701 with the birth of Anders Celsius, but three generations earlier with another Celsius, Anders’ grandfather Magnus Celsius. By doing so, Ekman effectively traces the importance of a scientific family’s genealogy and successive inheritance within the Celsius family of academic positions as astronomers. Anders Celsius’ career started with interests in mathematics, but soon turned to astronomy, which at that time encompassed other fields of geophysics. As early as 1722, Celsius showed a predilection for making and chronicling geophysical observations and had begun to accumulate important time series of meteorological data including temperature and pressure. In 1730, at age 29, and after years of unpaid work as an assistant, Celsius was appointed professor of astronomy at the University of Uppsala. With his professorship came an opportunity for a tour abroad. Celsius’ tour involved Germany, Italy, France, and England, but was most influenced by his connection to the Paris Observatory, where science was relatively advanced. In Paris he also became involved with the controversy on the shape of the Earth between Newton (who argued for an oblate spheroid flattened at the poles) and Cassini (who argued for a prolate spheroid flattened at the Equator). The controversy was to be solved by making meridian arc measurements at separated latitudes, one at the Equator and the other at a northern site. Celsius suggested a northern Swedish site near the Gulf of Bothnia and was immediately made a member of the expedition. The book goes into considerable, but rewarding, detail on the expedition, including challenges of travelling and living in the north in the early 1700s, the meticulous triangulation measurements, and pendulum gravity measurements. This expedition, as we now know, confirmed that Newton was correct. Back at home in Uppsala, Celsius assumed his role of professor of astronomy and raised money to build the Uppsala Observatory, still standing today. He equipped the observatory with angle instruments, telescopes, thermometers, barometers, magnetic compasses, and in particular a pendulum clock made in London by “the best clock-maker in Europe”. A series of chapters of the book are devoted to broad geophysical studies Celsius conducted that we do not normally associate with his name: precise latitude and longitude mapping in particular for the Uppsala Observatory; measuring gravity with his pendulum clock to study the flattening of the Earth; uplift of the land on the Swedish coast; sea level in relation to atmospheric pressure; and magnetic variations in time related to northern lights. Many of these studies, such as mapping, were undertaken to serve the needs of society, and thus one could call Celsius an early practitioner of applied geophysics. Ekman has also peppered his book with fascinating details that will resonate with multiple readers. Many who have lost data due to inadequate backup will empathize with Cel-