It has been truly said, that with our
large and powerful telescopic instruments we penetrate alike through the
boundaries of time and space: we measure the former through the latter, for
in the course of an
p 154
hour a ray of light traverses over a space of 592 millions of miles. While
according to the theogony of Hesiod, the dimensions of the universe were
supposed to be expressed by the time occupied by bodies in falling to the
ground ("the brazen anvil was not more than nine days and nine nights in
falling from heaven to earth"), the elder Herschel was of opinion* that
light required almost two millions of years to pass to the Earth from the
remotest luminous vapor reached by his forty-foot reflector.
[footnote] *"Hence it follows that the rays of light of the remotest
nebulae must have been almost two millions of years on their way, and that
consequently, so many years ago, this object must already have had an
existence in the sidereal heaven, in order to send out those rays by which
we now perceive it." William Herschel, in the 'Phil. Trans.' for 1802, p.
498. John Herschel, 'Astron.', 590. Arago, in the 'Annuaire', 1842, p.
334, 359, and 382-385.
Much, therefore, has vanished long before it is rendered visible to us --
much that we see was once differently arranged from what it now appears.
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