Prior to mercury, what substance was recommended for use in thermometers measuring air temperature?

“And if you want to know the hotness of the air and the relation between (temperature from) one day to another, prepare for yourself one of these two instruments”, begins a passage in a seventeenth-century Hebrew text. The ensuing description of a liquid-in-glass thermometer predates the earliest known sealed thermometer by nearly 30 years.

The 1629 book, entitled ‘Ma'yan Ganim (A Fountain of Gardens)’ was written by rabbi and physician Joseph Solomon Delmedigo, and contains the first known description of a sealed liquid thermometer. Two engravings alongside the text show an air thermometer and a sealed liquid thermometer. The liquid thermometer looks essentially the same as today’s mercury thermometers; however, the accompanying directions say to fill it with brandy.

For years, historians had credited the invention of the sealed thermometer to Ferdinand II, Grand Duke of Tuscany. In 1654, Ferdinand used a combination of brandy in, and lettering on, a sealed glass tube to create a device which allowed people to determine temperature changes by observing the movement of the booze.

Delmedigo (1591-1655) studied under Gallileo. He never took credit for the device he described. In fact, he was likely more of a journalist than a scientist. In an age when scientific journals were unknown, he spread news of discoveries across Europe by writing letters. Nevertheless, once Delmedigo's writings were properly translated, he was given credit for the sealed liquid thermometer.