These [binary stars] may serve another very important end.... Several stars of the first magnitude have been observed or suspected to have a proper motion; hence we may surmise that our sun, with all its planets and comets, may also have a motion towards some particular point of the heavens.... If this surmise should have any foundation, it will show itself in a series of some years in a kind of systematical parallax, or change due to the motion of the whole solar system.

Ch.4 "Life and Works" quote from "Researches on the Motion of the Sun and of the Solar System in Space" (1782). - Sir William Herschel: His Life and Works (1880)