Fig. 2. Comet feen 1744. From a drawing made at Cambridge.'

Fig. 3, The tail of a comet fo fituated, and feen fore-fhortened, turning downwards, that it fomewhat refembles a beard.

Fig. 4 and 5. Comets, whofe tails may be likened to a flaming fword. Many other forms fuggeft themfelves to a fertile imagination; that thefe vapours may vary in their properties is very fuppofable; but the general panic they have heretofore occafioned, together with the ftation from whence they were viewed, has been the most fruitful fource of tremendous and terrific appellations.

The tails of comets are fuppofed to be atmofpherical vapours furrounding thefe bodies, which are no fooner arrived fufficiently near the fun to feel his influence, than they bccome exceedingly rarified; and are extended proportionally to the heat of their fituation. They are extremely fine and pellucid, and permit the stars to be feen through them. The caufe of their afcent oppofite to the fun, is a difficulty, which feems beft anfwered by faying, they follow the impulfe of the folar rays; which, ftreaming from the fun, carry with them thefe extremely volatile particles through the free æther.

The vapours of the cometary tails have been calculated by obfervation, to be fo long as forty, fixty, or even eighty

millions of miles.

Comets, like planets, appear from the earth to be direct, flower than their real motion, retrograde, and ftationary, during fo much of their courfe as can be feen.

LECTURE

LECTURE VI.

Na former lecture, LADIES and GENTLEMEN, we ob

IN

served the very great distance of those heavenly bodies which yet we called our neighbours, and who, with ourselves, compofe one fyftem; Saturn is diftant, the Georgium Sidus diftant, the remoter extremes of the cometary orbits very distant ;-but what are thefe intervals to thofe of the ftars whofe fplendour we behold! whofe nearest estimation is four hundred thousand times the distance of the fun from us; this, I fay, is the estimated distance of the nearest; there are others, very, very much beyond; how noble then the powers of the mind! which not only speculates on thefe regions, but after vast additions of supposable space, repeated, and multiplied, feels its infinite remotenefs from the heaven of heavens!

The mind furveys a star in the zenith, or in the horizon; imagines itself present among a fyftem on the right hand, then (how swift is thought!) reverts to another on the left; thus it investigates fpace: by the ftars too, it investigates time; it conceives a period ere they exifted, ere one lambent flame illuminated the vast expanse; it conceives their revolu tions, their orbits, their periods, and, more than that, it awaits

their

their extinction, and diffolution. Darkness may again envelope the spheres, and every cheering ray withdraw; yet the human foul expects to furvive; and however it may witness the expiration of all things, to itself it arrogates immortality : and justly, for the heavens fhall decay, and be replaced by fucceffors; like fome magnificent prince, who changes to-day the garments of yesterday; fo the "Eternal as a vesture shall fold them up, and they fhall be changed." This fight we expect to fee ;-the very idea confutes the fuggeftions of those who think we are merely enlivened hovels of clay: no, the inhabitant and the building are different; a breeze may overthrow this, the fettling of a moth upon it may overweigh it; but the other fcorns the duration of time, and extends its existence parallel to eternity.

The diftances I have mentioned, LADIES and GENTLEMEN, though not beyond mental comprehenfion, are yet exceedingly difficult to reduce to regular, or proportionate measurement; the rapidity of a cannon ball is loft in the computation; the velocity of found, which is double that of a cannon ball, would require four million eight hundred thousand years to reach us; and light itself, which arrives from the fun in about eight minutes, is, during fix years, travelling from one of thefe ftars to us. So that should it please God to annihilate one of thefe luminaries, we fhould still continue, during fix years, to receive thofe beams it had previously emitted. After this obfervation, it feems almoft needless to mention, that they at least equal the fun in magnitude,