History of Science Museum: Collection Database Search


Time from the height of the sun

An altitude sundial uses the height rather than the direction of the sun to tell the time. In use, these dials need to be adjusted for the date, since the sun is higher in the sky in the summer than the winter. One of the most popular and long-lived forms is the cylinder or shepherd's dial [1]. Only a few portable sundials survive from ancient Rome [2 above], though versions of the vertical disc dial were still being made in the 17th century [3, 4 above]. Some designs of altitude dial were universal and could be used in any latitude [5], while others were specific to only one [6]. The top of the vertical leaf of [7] carries two small altitude dials with pin gnomons. But not every vertical dial is necessarily an altitude one: the main vertical dial of [7] uses the shadow cast by the string and depends on the sun's direction.

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