Artificiële horizon
Troughton & Simms, London, 1850
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When filled with mercury, this instrument functions as a perfectly horizontal reflecting surface and is essential for using a sextant on land.
An artificial horizon is necessary if, for example, on land one does not have a beautiful horizon but e.g. mountains. That is why the celestial body to be measured is reflected in a perfect horizontal mirror, e.g.; based on a spirit level, or, as here, a container filled with liquid mercury. This is covered with glass to prevent the wind from playing on this surface. If you want to measure the height of the sun or a star, you measure the angle between the sun and her reflection in the mirror. You simply have to divide that angle in two to get the height of the sun. For this they needed at least a sextant and preferably a Quintant that can measure up to 150°.