Convex lens mounted on a support

19 (lens diameter) 46 (total height)
Ebony and glass

INDEX 1788 : V.I.331

Lens similis, aqua lucis radii longius in focum colliguntur uplici annulo ligneo excepta, ut in orbem moveri possit, pedi insistens.

Similar lens, inside of a small wooden ring, by means of which rays of light converge at a further focus; which is supported on a stand so that it can move on the axle.

This accessory consists of a flat-convex lens, 19 cm in diameter and with 98 cm of focal distance (or an optical power approximately equal to 1 dioptric). The lens is mounted on a wooden support, capable of turning around its horizontal axis. The wooden hoop which surrounds the lens possesses a piece in brass, on the underside, ending in a small cylindrical piece which adapts to an orifice located on the support column. This system allows for the hoop and the lens to turn around a vertical axis.

From Colégio dos Nobres, catalogue n.º 321.

's Gravesande, William Jacob, Physices Elementa, Leiden, 1742, § 3565, Tab. CXV, fig.2.

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