93] Maedler showed that no part of the heavens
could be indicated as a region of exceptionally swift movements, such as
would result from the presence of a gigantic (though possibly obscure)
ruling body; but that a community of extremely sluggish movements
undoubtedly existed in and near the group of the Pleiades, where,
accordingly, he placed the centre of gravity of the Milky Way.[94] The
bright star Alcyone thus became the "central sun," but in a purely
passive sense, its headship being determined by its situation at the
point of neutralisation of opposing tendencies, and of consequent rest.
By an avowedly conjectural method, the solar period of revolution round
this point was fixed at 18,200,000 years.

The scheme of sidereal government framed by the Dorpat astronomer was,
it may be observed, of the most approved constitutional type;
deprivation, rather than increase of influence accompanying the office
of chief dignitary. But while we are still ignorant, and shall perhaps
ever remain so, of the fundamental plan upon which the Galaxy is
organised, recent investigations tend more and more to exhibit it, not
as monarchical (so to speak), but as federative. The community of proper
motions detected by Maedler in the vicinity of the Pleiades may
accordingly possess a significance altogether different from what he
imagined.

Bessel's so-called "foundation of an Astronomy of the Invisible" now
claims attention.[95] His prediction regarding the planet Neptune does
not belong to the present division of our subject; a strictly analogous
discovery in the sidereal system was, however, also very clearly
foreshadowed by him. His earliest suspicions of non-uniformity in the
proper motion of Sirius dated from 1834; they extended to Procyon in
1840; and after a series of refined measurements with the new Repsold
circle, he announced in 1844 his conclusion that these irregularities
were due to the presence of obscure bodies round which the two bright
Dog-stars revolved as they pursued their way across the sphere.[96] He
even assigned to each an approximate period of half a century. "I adhere
to the conviction," he wrote later to Humboldt, "that Procyon and Sirius
form real binary systems, consisting of a visible and an invisible star.
There is no reason to suppose luminosity an essential quality of
cosmical bodies. The visibility of countless stars is no argument
against the invisibility of countless others."[97]

An inference so