He also observed the eclipse of the sun on May 4, 1818.
Foretold that there would be a solar eclipse in that year, as stated by Herodotus.
In 1860 De la Rue took the photoheliograph to Spain for the purpose of photographing the total solar eclipse which occurred on the 18th of July of that year.
After a long eclipse it was finally re-established, though in a very modified form, by Alfonso Liguori about the middle of the 18th century.
Subtract 413 from 777, the remainder is 364; and 364 divided by four gives 91 without a remainder; consequently the eclipse happened in the fourth year of the ninety-first Olympiad, which is the date to which it is referred by Thucydides.