Gunter’s Quadrant, C 1750


English, c. 1750, the brass quadrant 11,5 cm in radius, set with twin pinhole sigh vanes and pierced with a hole for plumb line. The front is hand engraved unsigned, as described in 1623,It is laid out for vernal equinox of 10 March, consistent with the Julian calendar still in effect in England up to 1752, and for latitude of 51 1/2 °, consistent with London. Arranged as a quarter of an astrolabe, for a fixed latitude, the quadrant shows the sky projection between equator and tropics, crossed by the ecliptic (divided with a Zodiacal scale), horizon, azimuth lines, and hour lines. There is an edge scale of solar declination, a shadow square at the apex, a calendar scale, and a quadrantal scale for observing altitudes of sun and stars. The sky positions of five bright stars are plotted.

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