Selection of 26 eyepieces made by Sir William Herschel, 1780-1800.
© Science Museum / Science & Society Picture Library
In addition to building his own reflecting telescopes, Herschel (1738-1822) made his own micrometers. This measuring instrument uses a set of fixed and moveable wires to determine angular distances in the eyepiece of the telescope. In operation, the calibrated handle was used to move the parallel wires delineating the object being measured. The distance was then calculated from the number of turns of the handle which was attached to a fine threaded rod connected to the framework holding the moveable wires. Like Herschel's own eyepieces, the body of this instrument is made of cocoa, a tropical hardwood still used for woodwind instruments today.