Cassegrain reflecting Telescope of 2 1/2-inch aperture

Cassegrain reflecting brass telescope, 2½-inch aperture, with claw-foot pillar stand and divided object-lens micrometer, in original wooden case. Made by James Short, London, 1756–1758. Engraved "James Short London 224/908 = 9.6".

This reflecting telescope uses the Cassegrain optical configuration. Light is gathered by a large concave mirror and reflected onto a smaller convex mirror, which sends it back through a hole in the concave mirror to reach the eyepiece. Folding the light path this way allows a telescope with a long focal length to fit into a relatively short tube, making it ideal for observing the night sky.

James Short was a Scottish mathematician and manufacturer of optical instruments, specialising mainly in telescopes. His telescopes were sold across Britain, Europe and North America. They accompanied Captain Cook’s expedition to Tahiti for the observation of the 1769 Transit of Venus which was pivotal in the study of the solar system. A very similar Short telescope was also used by John Winthrop, professor of mathematics and philosophy at Harvard, to observe from North America the earlier Transit of Venus in 1761.

The numbers engraved on this example, 224/908 = 9.6, are part of James Short’s numbering system. They indicate that the telescope has a focal length of 9.6 inches, and that this example was the 224th of this type out of a total of 908 produced by Short.