t's tail), or a gaseous
and, so to speak, elementary form of luminous sidereal matter. Admitting
the existence of such a medium, Sir W. Herschel was led to speculate on
its gradual subsidence and condensation, by the effect of its own
gravity, into more or less regular spherical or spheroidal forms, denser
(as they must in that case be) towards the centre.

Assuming that in the progress of this subsidence local centres of
condensation subordinate to the general tendency would not be wanting,
he conceived that in this way solid nuclei might arise whose local
gravitation still further condensing, and so absorbing the nebulous
matter each in its immediate neighbourhood, might ultimately become
stars, and the whole nebula finally take on the state of a cluster of
stars.

Among the multitude of nebulae revealed by his telescope every stage of
this process might be considered as displayed to our eyes, and in every
modification of form to which the general principle might be conceived
to apply. The more or less advanced state of a nebula towards its
segregation into discrete stars, and of these stars themselves towards a
denser state of aggregation round a central nucleus, would thus be in
some sort an indication of age.

ALEXANDER VON HUMBOLDT

Cosmos, a Sketch of the Universe

Frederick Henry Alexander von Humboldt was born in Berlin on
September 14, 1769. In 1788 he made the acquaintance of George
Forster, one of Captain Cook's companions, and geological
excursions made with him were the occasion of his first
publications, a book on the nature of basalt. His work in the
administration of mines in the principalities of Bayreuth and
Anspach furnished materials for a treatise on fossil flora; and in
1827, when he was residing in Paris, he gave to the world his
"Voyage to the Equinoctial Regions of the New Continent," which
embodies the results of his investigations in South America. Two
years later he organised an expedition to Asiatic Russia, charging
himself with all the scientific observations. But his principal
interest lay in the accomplishment of that physical description of
the universe for which all his previous studies had been a
preparation, and which during the years 1845 to 1848 appeared under
the comprehensive title of "Cosmos, or Sketch of a Physical
Description of the Universe." Humboldt died on May 6, 1859.

_I.