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Some of these masses of light are indistinct and barely visible even by Herschel's forty-feet telescope; and he hence calculates, that if a mass thus traced out contain a cluster of five thousand stars, they must be eleven millions of millions of millions of miles off. M. Huygens entertained an analogous idea; and conceived that there are stars so immensely remote, that their light, although travelling at the rate of eleven millions of miles in a minute, and having thus continued to travel from the formation of the earth, or for nearly six thousand years, has not yet reached us.
But this sublime conception is of much earlier origin; and it is due to the magnificence of the Epicurean scheme to state that it is to be found completely developed amongst its principles. Lucretius has beautifully alluded to it in lines of which I must beg your acceptance of the following feeble translation, the only difference being, that lightning, or the electric fluid, is here employed instead of light, at least by Havercamp; for Vossius, in the Leyden edition, gives us light for lightning, reading lumina instead of fulmina.
The poet is speaking of the immensity of space :
The vast whole
What fancied scene can bound? O'er its broad realm,
Immeasured, and immeasurably spread,
From age to age resplendent lightnings urge,
In vain, their flight perpetual; distant, still,
* Omne quidem vero nihil est quod finiat extra. Est igitur natura loci, spatiumque profundi,
From this immense range of nebulous light Dr. Herschel derives comets, as well as stars and planets, believing them, indeed, to be the rudiments of the two latter; and he has especially noticed, as originating from this source, the well-remembered comet that so brilliantly, and for so long a period of time, visited our horizon during the close of the year 1811; which he conceives will be converted into a stellar or planetary orb as soon as its luminous matter, and especially that of its enormous tail, shall be sufficiently concentrated for this purpose. This tail he calculated, when at its greatest apparent stretch in October of the same year, at something more than a hundred millions of miles long, and nearly fifteen millions broad, though its bright or solid nucleus or planetary body was not supposed to measure more than four hundred and twentyeight miles. Its perihelion, or nearest approach to the sun, is stated at a distance of ninety-seven millions of miles, its distance from the earth at ninety-three millions. The comet of 1807 approached the earth within sixty-one millions of miles, or about a third nearer the earth, and that of 1680 within a sixth of its diameter, or as near as 147,000 miles, its tail being of a like length.
There is one comet, however, that we seem to be somewhat better acquainted with than with this
Quod neque clara suo percurrere fulmina cursu
Nec prorsum facere, ut restet minus ire, meando
*De Rer. Nat. i. 1000.
that paid us so near a visit, or indeed than with any ther, from its having approached us visibly for four times in succession, if not oftener. It was towards the beginning of last century that Mr. Halley was struck with the remark, that the general elements and character of the comets observed in 1531, 1607, and 1682, were nearly the same; whence he concluded that the whole formed but one identical body, that took about seventy-six years to complete its eccentric orbit; and hence, although in consequence of this eccentricity, and its travelling amidst a range of heavenly bodies that are altogether invisible to us, and whose influence seems to bid defiance to calculation, it is difficult to form an estimate of its progress, he ventured to suggest, that it would appear again, making due allowances for these incidents, towards the close of 1758, or the commencement of 1759: the time of its perihelion, as well as its other elements, he afterwards computed; and he had the high satisfaction of seeing his calculated prediction verified; the comet passing its perihelion March 12th, 1759, within the limits of the errors of which he thought his results susceptible. It is apparently this comet*, which at this last period only excited the curiosity of astronomers and mathematicians, that in 1456, or four revolutions earlier, towards the close of what are called the dark ages, spread such consternation over all Europe, already, indeed, terrified by the
* The same comet may be expected to appear again in the autumn of 1885. If the computations of astronomers are tolerably correct, it will be nearest the earth in the first week of October, and in its perihelion at the very beginning of November. - Ed.
rapid successes of the Turkish arms, that Pope Callixtus was induced to compose a prayer for the whole western church, in which both the Turks and the comet were included in one sweeping anathema.
According to this hypothesis, it is imagined possible that some of the lately discovered planets, which are now attendant upon the sun, were formerly comets, whose orbits have for ages been growing progressively more regular, as well as their constitutional rudiments more dense; and such, indeed, is the opinion of M. Voigt, and of various other philosophers on the Continent. But the whole of these must be regarded as mere speculations.
The object of the present and the preceding lecture has been to submit a sketch of the most obvious properties belonging to MATTER, so as to enable you to obtain a bird's eye view of the general phænomena it is capable of assuming, and the general changes it is necessarily sustaining. From the qualities I have placed before you, of passivity, cohesibility, divisibility, and attractions of various kinds, must necessarily result, according to the intensity with which they are called into action, the phænomena of liquidity, viscidity, toughness, elasticity, symmetry of arrangement, solidity, strength, and resilience. But the powers which thus perpetually build up the inorganic world, and to this our survey has been entirely confined, perpetually also destroy it for the whole, I wish you to bear in mind, is a continued circle of action; a circle most wise, most harmonious, most benevolent and hence, as one compound substance decays, another
springs up in its place, and can only spring up in consequence of such decay.
There is, however, another lesson, if I mistake not, which we may readily learn from these lectures, however imperfectly delivered, and which is altogether of a moral character: I mean that of humility, in regard to our own opinions and attainments; and of complacency, in regard to those of others. After a revolution of six thousand years, during the whole of which period of time the restless ingenuity of man has been incessantly hunting in pursuit of knowledge, what is there in natural philosophy that is thoroughly and perfectly known even at the present moment? and of the little that is thus known, what is there which has been acquired without the clash of controversy and the warfare of opposing speculations? Truth, indeed, -for ever praised be the great Source of Truth, for so eternal and immutable a decree,-has at all times issued, and at all times will issue, from the conflict; but while we behold philosophers of the highest reputation, philosophers equally balanced in the endowment of native genius, proved by the great teacher Time to have been alternately mistaken upon points to which they had honestly directed the whole acumen of their intellect, how absurd, how contemptible is the fond confidence of common life! Yet what, indeed, when fairly estimated by the survey that has now been briefly taken of the sensible universe,—what is the aggregate opinion, or the aggregate importance of the whole human race! We call ourselves lords of the visible creation: nor ought we at any time, with affected abjection, to degrade or despise the high gift of a rational and im