Benjamin Franklin (1706–1790) is best known as a statesman, inventor and writer, but he was no slouch as an Earth scientist, too.
In Franklin's day there was no such thing as a scientist (the word was first used by William Whewell in 1840), only "natural philosophers." At that time, science was pursued by gentlemen of leisure or by moonlighting professionals such as lawyers, clergymen and professors.
Not just a pure scientist, Franklin was relentlessly practical. His skill as an inventor relied on both a keen analytical mind and a strong drive to help the common people. Thus he gave away the lightning rod and the energy-efficient Franklin stove, refusing to patent their designs.
Franklin's Atmospheric and Ocean Science
When Franklin sold out his printing business at age 42, he began experimenting with electricity and making observations of the weather. Soon enough, he combined both interests by showing that lightning was natural electricity, a pioneering step in atmospheric science. Five years after he left the printing trade, Franklin was awarded the Copley Medal by the Royal Society of London for his electrical research.
Franklin also published observations of other atmospheric phenomena including storms and waterspouts. But his greatest geophysical legacy involved oceanography: he collected information from sailing ships that crossed the Atlantic, as well as during his own voyages, and published the first map of the Gulf Stream current in 1768.
Later in life, Franklin continued to publish observations and speculations on various natural events. In one brief paper he wrote in 1784 while in France, he is said to have proposed that the great eruption of Laki volcano in Iceland accounted for the unusually severe winter that followed. Because climate change is such a popular subject nowadays, Franklin is commonly called the first theorist of volcano-climate interactions.
Franklin and Volcanic Climate Change
I think that claim is a bit of a stretch, and you can judge for yourself, because the original paper is online. It's a rambling address, titled "Meteorological Imaginations and Conjectures," that opens with a paragraph about hailstones. Next he proposes a physical mechanism why the cold season begins and ends later than the sun's position in the sky would suggest: the ground stores solar heat to a considerable depth. This basic insight should make Franklin the father of borehole ground-temperature profiling, an important method of studying ancient climate.
Next comes the part that everyone cites. As a test of his solar-heating mechanism, he points to the weather during the summer of 1783, when a thick persistent haze covered Europe and part of North America. A magnifying glass wouldn't even burn paper, he said, so dim were the sun's rays. "Of course, their summer effect in heating the earth was exceedingly diminished. Hence the surface was early frozen. Hence the first snows remained on it unmelted, and received continual additions. Hence the air was more chilled, and the winds more severely cold. Hence perhaps the winter of 1783-4, was more severe, than any that had happened for many years."
What was the haze? He didn't know, and gave the question just one sentence: perhaps comet gases (a remarkable foresight of the Tunguska comet impact in 1908), perhaps smoke from the volcano in Iceland. But he concluded that whatever the haze is, people might want to plan for a cold winter after one appears. Franklin was thinking in the most practical terms, or so it seems.
In fact I think his paper shows a true scientist's refusal to speculate more than necessary. The source of the haze was not his concern—whereas the volcano in question was Laki, he lazily assumed it was Hekla (which had been dormant for 15 years). That's like confusing Italy's Vesuvio and Etna. All he knew was that this strange fog dimmed the sun, as measured by actual experiment. Nowadays scientists may lay claim to a speculative idea by slipping it into an unrelated paper, but that was not the style in Franklin's time.
Another telling sentence, one any scientist would recognize, was his call for more research: "It seems however worth the enquiry, whether other hard winters, recorded in history, were preceded by similar permanent and widely extended summer fogs." That keen nose for the next step makes Benjamin Franklin a thoroughly modern scientist.
PS: Franklin looked out his Paris window one day in 1783 and saw a hot-air balloon rising into the air carrying two passengers—the first humans to fly. He followed the experiments closely; they must have appealed to the man who once flew a kite in a thunderstorm. Once when a bystander asked what use these balloons were, he replied, "A quoi sert un enfant nouveau-né?" (What use is a new-born baby?) For more on this invention, see the About Inventors Guide, Mary Bellis.