Volume I Part 6 (1/2)
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!