Universal equatorial telescope. Diagram showing the mechanism of an equatorial mount for a telescope. An equatorial mount is used to track an astronomical object across the sky. Compared with other mounts, an equatorial mount is aligned with the Earth's axis of rotation, ensuring that adjustments only need be made around one axis and can be done at a constant speed rather than a variable speed. The first equatorial mount was invented by the British astronomer William Lassell (1799-1880). This artwork is the frontispiece to a book by the English opticians John and Peter Dollond, Descriptions and Uses of the Newly Invented Universal Equatorial Instrument (1772)