Instructions for use of the astronomical rotula by Thomas Jones, 1818.
© Science Museum / Science & Society Picture Library
This explanatory sheet gives instructions for the use of an astronomical instrument produced by Thomas Jones a London instrument maker. Consisting of circular rotating dials (vovelles) the device was used to determine the position of the Sun and Moon in the heavens. It is based on an instrument called an astronomical rotula, which was designed by the astronomy lecturer, James Ferguson (1710-1776) in 1739. It could also be used to find the dates of solar and lunar eclipses along with times of sunset and sunrise.