[footnote] *In December, 1837, Sir John Herschel saw the star [Greek symbol] Argo, which till that time appeared as of the second magnitude, and liable to no change, rapidly increase till it became of the first magnitude. In January, 1838, the intensity of its light was equal to that of 'a' Centauri. According to our latest information, Maclear in March, 1843, found it as bright as Canopus; and even 'a' Crucis looked faint by [Greek symbol] Argo. These events in the universe belong, however, with reference to their historical reality, to other periods of time than those in which the phenomena of light are first revealed to the inhabitants of the Earth: they reach us like the voices of the past. 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. The aspect of the starry heavens presents us with the spectacle of that which is only apparently simultaneous, and however much we may endeavor, by the aid of optical instruments, to bring the mildly-radiant vapor of nebulous masses or the faintly-glimmering starry clusters nearer, and diminish the thousands of years interposed between us and them, that serve as a criterion of their distance, it still remains more than probable, from the knowledge we possess of the velocity of the transmission of luminous rays, that the light of remote heavenly bodies presents us with the most ancient perceptible evidence of the existence of matter. It is thus that the reflective mind of man is led from simple premises to rise to those exalted heights of nature, where in the light-illumined realms of space, "myriads of worlds are bursting into life like the grass of the night."*