I was inspired to write this post by a visit to the archives of the Met Office in Exeter. The collections hold some absolutely fantastic items, including a printed proclamation issued by Charles II in the mid-1660s ordering a day of fasting and prayer in an attempt to stop the terrible deluge of rain the kingdom was experiencing (which, following the wettest winter on record in the UK, certainly struck a chord with me). As you might expect, Hooke and his Royal Society colleagues were extremely interested in the weather. Hooke and Christopher Wren invented instruments to measure and record weather conditions, and Hooke and a host of natural philosophers across Europe kept detailed weather diaries, sometimes spanning decades. Hooke himself wrote a series of instructions about how best to do this. As well as recording temperature, wind direction and strength, and so on, Hooke suggested that weather-observers note the ‘Constitution & face of the Sky’ as well as any other notable features such as any ‘haloes or Rings’ that might encircle the sun or moon. One problem, though, was the lack of a standard set of descriptions for cloud formations. So Hooke set about creating his own classification scheme.