He also observed the eclipse of the sun on May 4, 1818.
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.
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.
In the case of any subject-kind, its definition and its existence being avouched by vas, "heavenly body" for example, the problem is, given the fact of a non-self-subsistent characteristic of it, such as the eclipse of the said body, to find a ground, a / .t aov which expressed the a'irwv, in virtue of which the adjectival concept can be exhibited as belonging to the subjectconcept Kau' a&rO in the strictly adequate sense of the phrase in which it means also?7 abrO.
For the Algol variables it is possible to form even more direct calculations of the density, for from the duration of the eclipse an approximate estimate of the size of the star may be made.