two other comets appeared; the course of one of which had the wonderful variation of moving from east to west. Olbers has also calculated, that a comet will, after a lapse of 83,000 years approach as near to us as the moon: and that it will gravitate within 7700 geographical miles of the earth in 4,000,000 years, when, if its attraction is equal to that of the earth, the waters of the ocean will rise not less than 13,000 feet!

Since first the penetrating eye of man
Beheld thee rising o'er the balmy skirts
Of blooming Eden, thou art still the same;
And all now gaze on that, which Adam saw !
Adam and Moses, Thales, and the man,†
Who first taught Nature to th' astonish'd sons
Of western regions.-Oh! transporting thought!
To think that these unhallow'd eyes have seen
What Adam, Moses, and great Newton saw!

But all beneath the constant moon decay!—
All change!-all spring from infancy to age;
And at the appointed season of decay,
Melt into dust :-to be reform'd again.
Reform'd in splendour more magnificent,

Than eye has seen, or ear has ever heard!

And by that power OMNIPOTENT, whose name,

Inscrib'd on all the universe, proclaims

HIM PAST, HIM PRESENT, FUTURE, AND SOLE CAUSE,

SOLE POWER, Sole love, sole WISDOM, AND SOLE END!

Hymn to the Moon:

* The Moon.

+ Pythagoras.

CHAPTER VIII.

There is no animal, vegetable, or even mineral, but what sustains increase or diminution of weight every moment. They are either expanded by heat; contracted by cold; or affected by the substances, with which they are combined. It is no proof of the contrary to this position, that many of these changes are neither visible to the human eye; nor sensible to human touch. Animals and vegetables sustain these changes even oftener, than every thousandth part of a second. Gold, platina, and silver are less liable to change than other metals: but even their changes are frequently apparent. The ten simple earths are not only incapable of being analyzed into other bodies; but they are equally unsusceptible of being converted into each other. They are also incombustible and infusible and they enter into the composition of all substances that fill up the space, beginning with gems, and finishing with the smallest grain of sand. Even these have perpetual increase and diminution, Some minerals impart their virtues without losing any of their sensible weight;-but they lose weight nevertheless. It is only insensible to us.

The diamond is the most unchangeable of earthly bodies, when remaining in its quarry; and yet this hardest of all bodies is a combustible substance, and furnishes pure charcoal :-and charcoal itself, the most obstinate of all bodies, may be melted by the gas blowpipe.

The apparent changes in mineral bodies are exceedingly curious and beautiful. If nitric acid is poured on copper filings, the particles of copper will combine with those of the acid, and form a new body, distinct from either.

Mercury will dissolve in vapour in the common temperature of the atmosphere; or be shaken into dust. Iron is burnt by pure oxygen gas; and, when applied to a roll of sulphur, becomes obsequious and pulverizes. Gold and silver may be reduced to a calx; and then reclaimed to their primitive nature and form: and all bodies resolve themselves by chemical analysis into earth, water, salt, sulphur, or mercury. Shells, wherever found, in the sea, in rivers, or on the backs of animals, will ferment with acids and burn into lime.'

Silver is generally found combined with lead, antimony, and sulphur. Copper with many substances; iron mostly with sulphuric and carbonic acids:pyrites with iron and sulphur:-tin with sulphur and copper:-lead with sulphur and silver. Mercury is found among ores, stones, and clay; Nickel with iron and arsenic;-zinc with carbonic and sulphuric acids; -arsenic with iron, gold, and silver; and cobalt with arsenic and sulphuric acids. Of these gold and platina are the most unchangeable ;-they are dissolved by oxygenated muriatic acid;―silver and other metals by nitric acid; and they all burn readily in oxygen gas.

Limestone is formed by a combination of water and carbonic.— When a limestone rock appears, therefore, we may rest assured, that water once flowed there. Indeed the whole form and disposition of the earth prove, that it was once in a state of fluidity.

Sulphur, plumbago, the several bitumens, coal, jet, and amber, are combustible; and, therefore, freely change their forms and nature. The harder metals are combined by the force of chemical affinity; and decomposed by the same principle;-a power, supposed to arise from positive and negative electricity.

II.

Some have even affected, not only to separate the component parts of objects-the science of chemistrybut even to change one body into another. The industry of alchymists took this direction :-hence their endeavours to discover a menstruum, which, being cast upon metals in a state of infusion, would convert their true mercurial parts into gold. This menstruum they called the powder of projection. The possibility of metals being transmuted into gold was entertained by Bacon; and, in some measure, countenanced by Boyle and Newton. The changes of mineral bodies may be supposed to arise from an union of the combined effects of electricity, magnetism, and chemical affinity.

Paracelsus and Van Helmont took a less objectionable ground, when they insisted, that in Nature there existed a fluid, which has the power of reducing all bodies into their original elements. The existence of such a fluid is doubtless not impossible; but it has never yet been discovered: and if it really exist, it

1 Davy affirms, that elementary bodies are but few; and that even those few may, possibly, be only one under different forms.

will, most probably, be given to accident to discover. Nature has trusted no animal with fire, but man; an universal dissolvent would be too powerful a an agent for men to be entrusted with. The time may, however, come, when Nature may condescend to speak a more intelligible language, and entrust posterity with greater prerogatives. Indeed the time seems rapidly approaching for M. Lussac has discovered the means of rendering the most inflammable substances combustible without flame or fire. By means of the gas-blowpipe rock chrystal may be melted into a substance resembling pure mercury; rubies, sapphires, and emeralds may be melted into one mass; and even magnesia and pure carbonate of lime, long supposed to be the most refractory substances to fuse, may be melted by it. This astonishing power is derived, as Clarke has demonstrably proved, from the mixture of hydrogen gas with that of oxygen gas, in the exact proportion, in which they form water. By this art of burning the gaseous constituents of water, all things in Nature become fusible; and, in many instances, even volatizible.

Mercury is said to be the foundation of colours2; salt of savours; and sulphur of odours. Sulphur has such affinities, that it is found combined not only with minerals, but with vegetable and animal substances.

Two parts by bulk of hydrogen gas added to one part of oxygen gas. 2 Metals in a voltaic battery burn with various colours :-zinc with aj bluish light, fringed with red: silver, emerald green: lead emits a purple light copper, a bluish light with sparks. gold, white tinged with blue.