gravity, Mercury perihelion advance
Zeitschrift für Mathematik und Physik [translation]
Gravitational phenomena are the only effects concerning separate bodies for which we cannot prove that the intervening space has a role, i.e. the existence of changes that are communicated through it from one place to another. All the more understandable therefore is the hope that we will ultimately succeed in finding the missing evidence. However we must not regard the matter as if there was no doubt that this exception was only an appearance.