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A clear vision

This brass, leather and mahogany telescope, made in about 1770, allowed its user to see distant objects closely and clearly.

A telescope, set out in parts on a surface. All of the parts are arranged diagonally across the image, from top right to bottom left. The uppermost part is the dark leather case, split open along its length. Under it is the wooden telescope sleeve. The ends of the sleeve are cracked and the surface is mottled with dark and light areas. Under the sleeve are metal cylindrical sections, one long and two short. The short section at the right has a lght coloured outer layer, wooden in appearance. Under those sections are three more components. One is a cylinder containing a lense, one is a metal ring eyepiece and the other is a lense cap.

The telescope's parts (clockwise from top): leather casing, a mahogany inner tube, two joining pieces, the lens cap, lens and two eyepieces. Photo: George Serras.

The telescope is fitted with an achromatic lens. Before the invention of the achromatic lens in the mid-1700s, anyone looking through a telescope saw a blurry image surrounded by coloured fringes. This made accurate scientific and navigational observation impossible. In 1758, John Dollond, the London optician whose family company made this telescope, patented a lens that corrected these distortions, allowing sailors to finally take the accurate readings of the moon and stars needed to establish their longitude.

It is believed that this telescope belonged to John Gore (1728/9–1790), an American-born Royal Navy officer who sailed to the Pacific four times between 1764 and 1780 under captains Byron, Wallis, Cook and Clerke. The telescope would have greatly assisted him in his duties, which included scientific observation, navigation, shore landings and keeping watch.

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