Anemoscope

An anemoscope is a device invented to show the direction of the wind, or to foretell a change of wind direction or weather.

Hygroscopic devices, in particular those utilizing catgut, were considered as very good anemoscopes, seldom failing to foretell the shifting of the wind. The ancient anemoscope seems, by Vitruvius's description of it, to have been intended to show which way the wind actually blew, rather than to foretell into which quarter it would change.