The Botanic Garden Volume I Part 6

In some of these nodules there is a nucleus of whiter iron-earth surrounded by many concentric strata of darker and lighter iron-earth alternately. In one, which now lies before me, the nucleus is a prism of a triangular form with blunted angles, and about half an inch high, and an inch and half broad; on every side of this are concentric strata of similar iron-earth alternately browner and less brown; each stratum is about a tenth of an inch in thickness and there are ten of them in number. To what known cause can this exactly regular distribution of so many earthy strata of different colours surrounding the nucleus be ascribed? I don't know that any mineralogists have attempted an explanation of this wonderful phenomenon. I suspect it is owing to the polarity of the central nucleus. If iron-filings be regularly laid on paper by means of a small sieve, and a magnet be placed underneath, the filings will dispose themselves in concentric curves with vacant intervals between them. Now if these iron-filings are conceived to be suspended in a fluid, whose specific gravity is similar to their own, and a magnetic bar was introduced as an axis into this fluid, it is easy to foresee that the iron filings would dispose themselves into concentric spheres, with intervals of the circ.u.mnatant fluid between them, exactly as is seen in these nodules of iron-earth. As all the lavas consist of one fourth of iron, (Kirvan's Mineral) and almost all other known bodies, whether of animal or vegetable origin, possess more or less of this property, may not the distribution of a great portion of the globe of the earth into strata of greater or less regularity be owing to the polarity of the whole?]

[_And turn to adamant_. l. 192. The circ.u.mstances which render iron more valuable to mankind than any other metal are, 1. its property of being rendered hard to so great a degree and thus const.i.tuting such excellent tools. It was the discovery of this property of iron, Mr. Locke thinks, that gave such pre-eminence to the European world over the American one.

2. Its power of being welded; that is, when two pieces are made very hot and applied together by hammering, they unite compleatly, unless any scale of iron intervenes; and to prevent this it is usual for smiths to dip the very hot bar in sand, a little of which fuses into fluid gla.s.s with the scale and is squeezed out from between the uniting parts by the force of hammering. 3. Its power of acquiring magnetism.

It is however to be wished that gold or silver were discovered in as great quant.i.ty as iron, since these metals being indestructible by exposure to air, water, fire or any common acids would supply wholesome vessels for cookery, so much to be desired, and so difficult to obtain, and would form the most light and durable coverings for houses, as well as indestructible fire-grates, ovens, and boiling vessels. See additional notes, No. XVIII. on Steel.]

"Last MICh.e.l.l'S hands with touch of potent charm The polish'd rods with powers magnetic arm; 195 With points directed to the polar stars In one long line extend the temper'd bars; Then thrice and thrice with steady eye he guides, And o'er the adhesive train the magnet slides; The obedient Steel with living instinct moves, 200 And veers for ever to the pole it loves.

[_Last Mich.e.l.l's hands_. l. 193. The discovery of the magnet seems to have been in very early times; it is mentioned by Plato, Lucretius, Pliny, and Galen, and is said to have taken its name of magnes from Magnesia, a sea-port of antient Lybia.

As every piece of iron which was made magnetical by the touch of a magnet became itself a magnet, many attempts were made to improve these artificial magnets, but without much success till Servingdon Savary, Esq. made them of hardened steel bars, which were so powerful that one of them weighing three pounds averdupois would lift another of the same weight. Philos. Trans.

After this Dr. Knight made very successful experiments on this subject, which, though he kept his method secret, seems to have excited others to turn their attention to magnetism. At this time the Rev. Mr. Mich.e.l.l invented an equally efficacious and more expeditious way of making strong artificial magnets, which he published in the end of the year 1750, in which he explained his method of what he called "the double touch", and which, since Mr. Knight's method has been known, appears to be somewhat different from it.

This method of rendering bars of hardened steel magnetical consists in holding vertically two or more magnetic bars nearly parallel to each other with their opposite poles very near each other (but nevertheless separated to a small distance), these are to be slided over a line of bars laid horizontally a few times backward and forward. See Mich.e.l.l on Magnetism, also a detailed account in Chamber's Dictionary.

What Mr. Mich.e.l.l proposed by this method was to include a very small portion of the horizontal bars, intended to be made magnetical, between the joint forces of two or more bars already magnetical, and by sliding them from end to end every part of the line of bars became successively included, and thus bars possessed of a very small degree of magnetism to begin with, would in a few times sliding backwards and forwards make the other ones much more magnetical than themselves, which are then to be taken up and used to touch the former, which are in succession to be laid down horizontally in a line.

There is still a great field remains for future discoveries in magnetism both in respect to experiment and theory; the latter consists of vague conjectures the more probable of which are perhaps those of Elpinus, as they a.s.simulate it to electricity.

One conjecture I shall add, viz. that the polarity of magnetism may be owing to the earth's rotatory motion. If heat, electricity, and magnetism are supposed to be fluids of different gravities, heat being the heaviest of them, electricity the next heavy, and magnetism the lightest, it is evident that by the quick revolution of the earth the heat will be acc.u.mulated most over the line, electricity next beneath this, and that the magnetism will be detruded to the poles and axis of the earth, like the atmospheres of common air and of inflammable gas, as explained in the note on Canto I. l. 123.

Electricity and heat will both of them displace magnetism, and this shows that they may gravitate on each other; and hence when too great a quant.i.ty of the electric fluid becomes acc.u.mulated at the poles by descending snows, or other unknown causes, it may have a tendency to rise towards the tropics by its centrifugal force, and produce the northern lights. See additional notes, No. I.]

"Hail, adamantine STEEL! magnetic Lord!

King of the prow, the plowshare, and the sword!

True to the pole, by thee the pilot guides His steady helm amid the struggling tides, 205 Braves with broad sail the immeasurable sea, Cleaves the dark air, and asks no star but Thee.-- By thee the plowshare rends the matted plain, Inhumes in level rows the living grain; Intrusive forests quit the cultured ground, 210 And Ceres laughs with golden fillets crown'd.-- O'er restless realms when scowling Discord flings Her snakes, and loud the din of battle rings; Expiring Strength, and vanquish'd Courage feel Thy arm resistless, adamantine STEEL!

215 4. "HENCE in fine streams diffusive ACIDS flow, Or wing'd with fire o'er Earth's fair bosom blow; Trans.m.u.te to glittering Flints her chalky lands, Or sink on Ocean's bed in countless Sands.

Hence silvery Selenite her chrystal moulds, 220 And soft Asbestus smooths his silky folds; His cubic forms phosphoric Fluor prints, Or rays in spheres his amethystine tints.

Soft cobweb clouds transparent Onyx spreads, And playful Agates weave their colour'd threads; 225 Gay pictured Mochoes glow with landscape-dyes, And changeful Opals roll their lucid eyes; Blue lambent light around the Sapphire plays, Bright Rubies blush, and living Diamonds blaze.

[_Diffusive Acids flow_. l. 215. The production of marine acid from decomposing vegetable and animal matters with vital air, and of nitrous acid from azote and vital air, the former of which is united to its basis by means of the exhalations from vegetable and animal matters, const.i.tute an a.n.a.logy which induces us to believe that many other acids have either their bases or are united to vital air by means of some part of decomposing vegetable and animal matters.

The great quant.i.ties of flint sand whether formed in mountains or in the sea would appear to derive its acid from the new world, as it is found above the strata of lime-stone and granite which const.i.tute the old world, and as the earthy basis of flint is probably calcareous, a great part of it seems to be produced by a conjunction of the new and old world; the recrements of air-breathing animals and vegetables probably afford the acid, and the sh.e.l.ls of marine animals the earthy basis, while another part may have derived its calcareous part also from the decomposition of vegetable and animal bodies.

The same mode of reasoning seems applicable to the siliceous stones under various names, as amethyst, onyx, agate, mochoe, opal, &c. which do not seem to have undergone any process from volcanic fires, and as these stones only differ from flint by a greater or less admixture of argillaceous and calcareous earths. The different proportions of which in each kind of stone may be seen in Mr. Kirwan's valuable Elements of Mineralogy. See additional notes, No. XIX.]

[_Living diamonds blaze_. l. 228. Sir Isaac Newton having observed the great power of refracting light, which the diamond possesses above all other crystallized or vitreous matter, conjectured that it was an inflammable body in some manner congealed. Insomuch that all the light is reflected which falls on any of its interior surfaces at a greater angle of incidence than 241/2 degrees; whereas an artificial gem of gla.s.s does not reflect any light from its hinder surface, unless that surface is inclined in an angle of 41 degrees. Hence the diamond reflects half as much more light as a fact.i.tious gem in similar circ.u.mstances; to which must be added its great transparency, and the excellent polish it is capable of. The diamond had nevertheless been placed at the head of crystals or precious stones by the mineralogists, till Bergman ranged it of late in the combustible cla.s.s of bodies, because by the focus of Villette's burning mirror it was evaporated by a heat not much greater than will melt silver, and gave out light. Mr.

Hoepfner however thinks the dispersion of the diamond by this great heat should be called a phosph.o.r.escent evaporation of it, rather than a combustion; and from its other a.n.a.logies of crystallization, hardness, transparency, and place of its nativity, wishes again to replace it amongst the precious stones. Observ. sur la Physique, par Rozier, Tom.

x.x.xV. p. 448. See new edition of the Translation of Cronsted, by De Costa.]

"Thus, for attractive earth, inconstant JOVE 230 Mask'd in new shapes forsook his realms above.-- First her sweet eyes his Eagle-form beguiles, And HEBE feeds him with ambrosial smiles; Next the chang'd G.o.d a Cygnet's down a.s.sumes, And playful LEDA smooths his glossy plumes; 235 Then glides a silver Serpent, treacherous guest!

And fair OLYMPIA folds him in her breast; Now lows a milk-white Bull on Afric's strand, And crops with dancing head the daisy'd land.-- With rosy wreathes EUROPA'S hand adorns 240 His fringed forehead, and his pearly horns; Light on his back the sportive Damsel bounds, And pleased he moves along the flowery grounds; Bears with slow step his beauteous prize aloof, Dips in the lucid flood his ivory hoof; 245 Then wets his velvet knees, and wading laves His silky sides amid the dimpling waves.

While her fond train with beckoning hands deplore, Strain their blue eyes, and shriek along the sh.o.r.e; Beneath her robe she draws her snowy feet, 250 And, half-reclining on her ermine seat, Round his raised neck her radiant arms she throws, And rests her fair cheek on his curled brows; Her yellow tresses wave on wanton gales, And high in air her azure mantle sails.

255 --Onward He moves, applauding Cupids guide, And skim on shooting wing the s.h.i.+ning tide; Emerging Triton's leave their coral caves, Sound their loud conchs, and smooth the circling waves, Surround the timorous Beauty, as she swims, 260 And gaze enamour'd on her silver limbs.

--Now Europe's shadowy sh.o.r.es with loud acclaim Hail the fair fugitive, and shout her name; Soft echoes warble, whispering forests nod, And conscious Nature owns the present G.o.d.

265 --Changed from the Bull, the rapturous G.o.d a.s.sumes Immortal youth, with glow celestial blooms, With lenient words her virgin fears disarms, And clasps the yielding Beauty in his arms; Whence Kings and Heroes own ill.u.s.trious birth, 270 Guards of mankind, and demiG.o.ds on earth.

[_Inconstant Jove_. l. 229. The purer air or ether in the antient mythology was represented by Jupiter, and the inferior air by Juno; and the conjunction of these deities was said to produce the vernal showers, and procreate all things, as is further spoken of in Canto III. l. 204.

It is now discovered that pure air, or oxygene, uniting with variety of bases forms the various kinds of acids; as the vitriolic acid from pure air and sulphur; the nitrous acid from pure air and phlogistic air, or azote; and carbonic acid, (or fixed air,) from pure air and charcoal.

Some of these affinities were perhaps portrayed by the Magi of Egypt, who were probably learned in chemistry, in their hieroglyphic pictures before the invention of letters, by the loves of Jupiter with terrestrial ladies. And thus physically as well as metaphysically might be said "Jovis omnia plena."]

VI. "GNOMES! as you pa.s.s'd beneath the labouring soil, The guards and guides of Nature's chemic toil, YOU saw, deep-sepulchred in dusky realms, Which Earth's rock-ribbed ponderous vault o'erwhelms, 275 With self-born fires the ma.s.s fermenting glow, And flame-wing'd sulphurs quit the earths below.

[_With self-born fires_. l. 275. After the acc.u.mulation of plains and mountains on the calcareous rocks or granite which had been previously raised by volcanic fires, a second set of volcanic fires were produced by the fermentation of this new ma.s.s, by which after the salts or acids and iron had been washed away in part by elutriation, dissipated the sulphurous parts which were insoluble in water; whence argillaceous and siliceous earths were left in some places; in others, bitumen became sublimed to the upper part of the stratum, producing coals of various degrees of purity.]

1. "HENCE ductile CLAYS in wide expansion spread, Soft as the Cygnet's down, their snow-white bed; With yielding flakes successive forms reveal, 280 And change obedient to the whirling wheel.

--First CHINA'S sons, with early art elate, Form'd the gay tea-pot, and the pictured plate; Saw with illumin'd brow and dazzled eyes In the red stove vitrescent colours rise; 285 Speck'd her tall beakers with enamel'd stars, Her monster-josses, and gigantic jars; Smear'd her huge dragons with metallic hues, With golden purples, and cobaltic blues; Bade on wide hills her porcelain castles glare, 290 And glazed PaG.o.das tremble in the air.

[_Hence ductile clays_ l. 277. See additional notes, No. XX.]

[_Saw with illumin'd brow_. l. 283. No colour is distinguishable in the red-hot kiln but the red itself, till the workman introduces a small piece of dry wood, which by producing a white flame renders all the other colours visible in a moment.]

[_With golden purples_. l. 288. See additional notes, No. XXI.]

"ETRURIA! next beneath thy magic hands Glides the quick wheel, the plaistic clay expands, Nerved with fine touch, thy fingers (as it turns) Mark the nice bounds of vases, ewers, and urns; 295 Round each fair form in lines immortal trace Uncopied Beauty, and ideal Grace.

[_Etruria! next_. l. 291. Etruria may perhaps vie with China itself in the antiquity of its arts. The times of its greatest splendour were prior to the foundations of Rome, and the reign of one of its best princes, Ja.n.u.s, was the oldest epoch the Romans knew. The earliest historians speak of the Etruscans as being then of high antiquity, most probably a colony from Phoenicia, to which a Pelasgian colony acceded, and was united soon after Deucalion's flood. The peculiar character of their earthern vases consists in the admirable beauty, simplicity, and diversity of forms, which continue the best models of taste to the artists of the present times; and in a species of non-vitreous encaustic painting, which was reckoned, even in the time of Pliny, among the lost arts of antiquity, but which has lately been recovered by the ingenuity and industry of Mr. Wedgwood. It is supposed that the princ.i.p.al manufactories were about Nola, at the foot of Vesuvius; for it is in that neighbourhood that the greatest quant.i.ties of antique vases have been found; and it is said that the general taste of the inhabitants is apparently influenced by them; insomuch that strangers coming to Naples, are commonly struck with the diversity and elegance even of the most ordinary vases for common uses. See D'Hancarville's preliminary discourses to the magnificent collection of Etruscan vases, published by Sir William Hamilton.]

"GNOMES! as you now dissect with hammers fine The granite-rock, the nodul'd flint calcine; Grind with strong arm, the circling chertz betwixt, 300 Your pure Ka-o-lins and Pe-tun-tses mixt; O'er each red saggars burning cave preside, The keen-eyed Fire-Nymphs blazing by your side; And pleased on WEDGWOOD ray your partial smile, A new Etruria decks Britannia's isle.-- 305 Charm'd by your touch, the flint liquescent pours Through finer sieves, and falls in whiter showers; Charm'd by your touch, the kneaded clay refines, The biscuit hardens, the enamel s.h.i.+nes; Each nicer mould a softer feature drinks, 310 The bold Cameo speaks, the soft Intaglio thinks.

[Ill.u.s.tration: _H. Webber init J. Holloway sculpt Copied from Capt.

Phillip's Voyage to Botany Bay, by permission of the Proprietor_]

[Transcriber's note: names of painter and engraver are only guesswork.]

[Ill.u.s.tration: AM I NOT A MAN AND A BROTHER]

"To call the pearly drops from Pity's eye, Or stay Despair's disanimating sigh, Whether, O Friend of art! the gem you mould Rich with new taste, with antient virtue bold; 315 Form the poor fetter'd SLAVE on bended knee From Britain's sons imploring to be free; Or with fair HOPE the brightening scenes improve, And cheer the dreary wastes at Sydney-cove; Or bid Mortality rejoice and mourn 320 O'er the fine forms on PORTLAND'S mystic urn.--

[_Form the poor fetter'd Slave_. l. 315. Alluding to two cameos of Mr.