glass

glass, the seaman's name for a telescope, a barometer, and—before clocks suitable for use on board ship were developed—a sand-glass. Although the word telescope is as old as the instrument itself, being used by Galileo in 1611 to describe his invention, the name did not become used in maritime circles until very much later. In 1619 there is a reference to it in England under the name ‘trunke-spectacle’, but the first naval use of the name appears to have been by Murdoch Mackenzie (b. 1712) in 1744 in his treatise on surveying (see also hydrography). In general maritime use the name glass was an abbreviation of long-glass or spyglass, and Captain Marryat was using that name in his naval novels at least as late as 1844.

The barometer was, and is, almost invariably known as a glass, even when in the form of a barograph, ‘the glass is high, low, rising, falling’ being the usual description of its movements.