Joseph Fourier, Glass, greenhouses, Venice, Horace de Saussere's hot box, greenhouse effect

Hi, I'm Ana, the Ethical Systems Nerd, with the March 21st episode of Nerd Nodes.

The United Nations Framework Convention on Climate Change came into effect on March 21, 1994. And today is the birthday in 1768 of Joseph Fourier1 , whose Fourier transform is one of the most useful mathematical tools of all time, with practical applications ranging from medical imaging to digital music to quickly approximating all sorts of very hard computations, and one which has tormented generations of physics students2 . On the other hand, Fourier also invented dimensional analysis, one of the greatest physics student cheat codes of all time3 . Dimensional analysis says that you can't compare apples to oranges because they are different units, but that you can be pretty confident your calculations are correct if the units all check out. Fourier is also the one who is first credited with suspecting that the Earth was warmer than could be accounted for purely by the radiation coming from the Sun.

In the eighteenth century, there were several technological advances in the manufacture of glass, which meant that larger panes of high quality clear glass were easier to produce, and so they became more widely available. If you were a wealthy European this meant you were installing lots of mirrors and greenhouses to show off your wealth and modernity, and you were also probably financing voyages around the world to steal exotic plants to fill your greenhouse with.

Then as now, industrial success relied on technological knowledge, access to raw materials, and finance. Venice was unparalleled in making luxury glass, with its impeccable local silica quartz plus its shipping empire to bring it Syrian soda ash (that is sodium carbonate, obtained by burning plants growing in salty soil) and dyes and colorings from around the trading world. As its expertise and reputation built up over the centuries, Venice tried to protect its trade secrets by prohibiting its glassmakers from leaving the Republic, a strategy that was doomed to fail.

England became a glassmaking powerhouse by the end of the 17th century, probably because a certain George Ravenscroft had parents who were secret Roman Catholics. George went to France to study to be a secret priest, attending a secret seminary, whose graduates went on to have a 33% martyrdom rate when they returned to England. George had a better idea, dropped out, and ended up in Venice, where he and two of his brothers started an import/export business specializing in fancy items like lace and Murano glass. Eventually, in 1666, George returned to England to run the business from there. Several people were trying to grow glassmaking as an industry in England, and George decided to join in. Through some combination of industrial espionage and experimentation, George and a Jewish glassmaker named da Costa from Piedmont in Northern Italy developed a new process for manufacturing glass from English flint, potash, and saltpetre plus the Italian secret ingredient of lead. Saltpetre turned out to help with manufacturing clear uncolored glass, so Her Ladyship's reflection wasn't tinted green.

Glass was a practical luxury item which could make beautiful goblets and baubles as well as light admitting windows and flattering reflective mirrors. And, clear glass at scale was a material whose impact on science would be almost unimaginable. From thermometers, to petri dishes and test tubes, to Erlenmeyer flasks, not to mention lenses, prisms, and mirrors, the applications of the moldable, inert, and transparent substance have been universal in the physical sciences, and are still being developed to this day.

Horace de Saussere, a naturalist from Geneva and the great-grandfather of the famous linguist, observed "it is a known fact, and a fact that has probably been known for a long time, that a room, a carriage, or any other place is hotter when the rays of the sun pass through glass." He designed a "hot box", what we would now call a solar oven, incorporating a sheet of glass topping a darkened chamber, which achieved temperatures of up to 230 degrees Fahrenheit, well above the boiling point of water.

In 1822, Joseph Fourier published his work The Analytic Theory of Heat. In an article in 1827 he wrote "The question of the terrestrial temperatures has always appeared to me to be one of the great objectives of cosmological studies, and I had it principally in view whilst establishing the mathematical theory of heat." 4 Fourier's theory of heat suggested that the Earth's comfortable temperatures could not be explained solely by the radiation coming from the Sun, or the other suspected causes. Fourier suggested that the Earth's atmosphere must act as an insulator, and so cause the Sun's heat to be trapped and to build up over time, as can be easily observed by anyone with glass in their carriage windows. Fourier referenced de Saussure's experiments with his "hot box" which, crucially, was shown to work in the same way at the top of a mountain as on the plain beneath.

So, yes, we have early experiments with solar energy to thank for the discovery of the Earth's atmospheric greenhouse effect, by way of Joseph Fourier whose mathematics has left very little of the modern world untouched, including the study of harmonics, speaking of which, also on March 21st, the birthday of one of the greatest composers in the history of Western music, and perhaps more impressively, one of the greatest composers in his own family, Johann Sebastian Bach was born in 1685, on March 21st.