Hygrometers – used to measure atmospheric humidity – have been used in some form for thousands of years; 2000 years ago during the Shang Dynasty, the Chinese used a bar of charcoal and a lump of earth: its dry weight was taken, then compared with its damp weight after being exposed in the air; the differences in weight were used to tally the humidity level.
A crude hygrometer was invented by Leonardo da Vinci in 1480. Even human hair was used in Hair Tension Hygrometers; the hair is hygroscopic (tending toward retaining moisture) and its length changes with humidity. The length change was magnified by a mechanism and indicated on a dial or scale.
Unsurprisingly, the lifecycle of a butterfly is very much affected by relative humidity. In its larval stage, the pupa of tropical species requires typical humidities of 80-90%. It forms its pupal skin according to this humidity. In Northern and Eastern species, however, the pupa can develop with far lower humidities, sometimes descending to 50-60%. Too much humidity, or too little, coupled with changes in temperature, can seriously hinder the emergence of the butterfly. Monarchs are an exception as they overwinter on the frost line in Mexico and have an inherent cool tolerance.
This new piece continues a conversation about the connection of nature and science, and of the delicate environmental balance which binds us all.
Morpho helena, antique hygrograph