How to construct a wonderful lantern that can reveal small inscriptions even at a long distance.

Make a lantern of cylindrical shape, as you can see in this illustration. Mount a concave mirror, whose form should correspond as close as possible to a parabolic curve, in upright position at the bottom of the lantern, AB. Put the flame of a candle at the focal point of the mirror, and so you have got what you wanted.

The lantern will shine with such a remarkable splendour, that it will, even at nighttime, without any difficulty reveal even the smallest inscriptions so that they can be inspected with the help of a telescope.

Those who look at the flame at distance will think that it comes from a huge fire. The effect of the light will be even stronger if the inner sides of the cylinder are covered with reflective tin at the ellipses. But the accompanying figure will demonstrate the construction clearly enough. E indicates the handle, D the window and C the chimney.

From Ars Magna Lucis & Umbrae, Ed 1, Rome 1646. Translated by Mats Rendel, B.A. © 2008.