Perpetual lamp, or inextinguishable lamp. Some of the moderns imagined that the ancients had lamps they locked inside tombs, and that their light lasted forever, because these lamps were filled with a kind of oil that never dissipated.

Among the examples they cited to support this error, the most famous is the one in the sepulcher of Tulia, daughter of Cicero, discovered under the pontificate of Paul III in 1540. It is said that in this tomb, as well as in those around Viterbe, many lamps that only expired when exposed to air were found; these are real fables, whose origins come from reports made by workmen hired to shove the dirt off these tombs. These workmen have seen a bit of smoke, a light flame or fire coming out of the monuments they were excavating, and having found lamps in the area, thought that these had just expired. Not much more was necessary to establish the eternal lamps , while it was only a phosphorous very common in our own cemeteries, and in places where we bury animals. This phenomenon is produced by the fat content, which, after being concentrated, escapes once in the presence of new air, subtilizes and ignites.

However, the false existence of inextinguishable lamps adopted by Pietro Sancti-Bartholi, gave us his collection of sepulchral lamps from the ancients, engraved in copper plate and subsequently illustrated with expert observations done by Bellori.

These two works were followed by the treaty of Fortunius Licetus, de lucernis antiquorum reconditis , in which he flaunted great erudition without teaching us the secret of the perpetual lamps . Cassiodore, who lay claim to possess it, did not persuade anyone; Kircher and Korndoffer were not any more successful. Joining them was abbot Trithemius, who assured that his oil of sulfur, borax and spirits could burn without any waste. The slightest dabbling in Physics is enough to refute all chimeras of the sort. There is neither oil that is not consumed when lit, nor wick that burns for a long time without fuel. It is true that the one made of asbestos illuminates without loss of substance and without being necessary to blow it out, but not without fuel, and not after its fuel has been consumed; it is an impossible marvel. The wick could burn for a year in the lamp of gold consecrated by Callimachus in Minerva’s temple, because the oil of this lamp was not allowed to dry out and because it was changed secretly. So, what Pausanias and Plutarch tell about the lamps consecrated in the temples of Diana and Jupiter Ammon, which burned for years on end without consuming oil, was based upon the stories invented by charlatan priests, interested in persuading the common people of these wonders.