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Show 12 CENTRAL FIRES. NoTEVL "Yvhich thouah the (1111 was confl:antly to illuminate two thirds of the globe at once, .., 1 ith ; heat :qual to that at the equator, it would foon become a ma:s o: folic\ icc. I_Iis rca fonings and calculations on this fubjcCl: are too long and too 1ntncat~ :o be w fcrted here, but are equally curious and· inge~ious and · carry much· corlVlcbon along' wi th them. The opinion that the centre of the earth conflfl:s of a brge mafs of burning Ian, has oecn efpoufcd by Boyle, Boerhave, and many other philo:ophers .. Some of whom c~nfiderin~ its fu ppofc;d efFeCl:s on vegetation and the formatiOn of mtnerals have callec.l1t a feconci"fun. There arc many arguments in fupport of this opinion. r. Becau fc the power of the fun does not extend much beyond ten feet deep into :he ea-rth, ~ll bel~w being in winter and fummer always of the fame degree of heat, VIZ. 48, . whrch bemg much wanner than the mildefl: frofl:, is fuppofed to be fufl:ained 'by fome internal difl:ant fi re. Add to this how~ver that from experiments made fome years ago by Di'. Frankl in the fpring-water at Philadelphia appeared to be of 51. of heat, which feems farther to confirm this opinion, !ince the climates in North America are fuppofed to be colder than thofe of Europe under fimilar d~grees of latitude. 2·. M. De Luc in going 1359 feet perpendicutar into the mines of Hartz on July the 5th, 1778, on a very fine day found the air at the bottom a little warmer than at the top of the lhaft. Phil. T ranf: Vol. LXIX. p. 488. In the mines in Hungary, which are )OO cubits deep, the heat becomes very troublefvme when the miners get below 4So feet depth. M ?rinus de L ocis jubier. p. 131. But as fome other deep mines as mentioned by Mr. Kirwan are faid to poffefs but the common heat of the earth; and as the crull: of the globe thus penetrated by human i'.lbour is fo thin compared with the whole, no certain deduction can be made from thefe faCl:s on either f1de of the quell:ioH. 3· The warm-fprings in many parts of the earth at great diftance from any volcanos feem to originate from the condenfation of v:~pours ariflng from water whid1 is boiled 'Ely fubterraneous fires, and cooled again in their paffage through a certaill rength of the colder foil; for the theory of chemical folution will not explain the equality of their heat at all feafons and through fo many centuries. See note on Fucus in Vol. II. See a letter on this fubjeB: in Mr. Pil kinton 's View ofDerby! hire from Dr. Darwin. 4·· From the fituatioBs of volcanos whic.h are a! ways found upon the fummit of the highcft mountains. For as thefe mountains have been lifted up ;wd lofe fevera.\ of their uppermofl: ftrata as they rife, the lowefl: fl:rata of the earth yet known appear at the tops of the highcfl: hills; and the beds of the volcanos upon thefe !tills muft in confequence belong to the lowefl: fl:rata of the earth, confllling 'perhap of grani te 0r bafaltes, which were produced before the exiftence of animal or ver,etable bodies, and might confl:.i.tute the original nucleus of the earth, which 1 have fupp~fed to have been projcCl:cd from the fun, hence the volcanos themfelves appear to be fpir acula or chimneys belonging to great central fires. It is probably owing to the efcape of the cbf1:ic vapours from thefe fpiracula that the modern earthquakes are of fuch fmall exocr. t compared with thofe of remote antiquity, of which the vdtiges remain all over the· globe. '). The great fizc and height of the G:ontinents, and the great fizc and depth of the South-fea, Atlantic, and other oceans, evince that the fir.[l. earthquakes, whi ..:h produced thcfe immcnfe changes in the globe, mufl: have been. occaGoncd by central fires. 6. The / NoTE VII. ELEMENTARY HEAT. 6. The very di(bnt and expeditious communication of the fh k f fc k Th h k oc 5 o orne great earth-qua es. . e ea~t qua e at Lilbon in 1755 was perceived in Scotland, in the Peak of D erby011re, and 111 many other difl:ant parts of Europe The pcrcuili f · Witlt b t th 1 . f r · • IOI1S 0 It trave 1l ed · 6 a ou edv e OCtty o •ound, VIZ. about thirteen mi les in a m"1nute · Th e can h qua k o · In1 I· 9d3 ·crx ten eel 26oo leagues. (Goldfinith's Hi £tory.) The•re, Ph e nomena are eafily ex p fa {mi c 1 the. central parts of the earth conflfl: of a fl "d J -. Ul ava, as a percuffion On one p:lr o uch a flllld mafs would be fel t on other parts of itsconfininQ" va It J'k 11 k t fl 'd t . d . bl dd "' II ' I e a lifO eon a lU l cdo n a1In e lhl1 a . a cr, which .h owe.v er gentle on 0 nc fi1d e · · IS percepttble to the hand p ace on tIC ot er ' and the v~l oc~ty wtth which fuch a concuffion would travel would be that of foundr or thir teen mdes 1n a minute F or f tJ · t: · · I li b . n. 1 d . . ur ler 111 ormatiOn on this part of Pt 1 e. u 1eGt t 1e rca er 1s .r eferred t iJ Mr. Michell 's excel !e n t T rea t1"f ie on earthquakes . 111 the hdof. Tranf. V0l. LI. 7· That there is a cJvity at the centre of the earth is d bable by the late e ·periments on the attraCl:ion of mountains hy Mr M fl !rna e pro- ~ r d f h r. . I • a {e yne, who bu pfpi ote . rom ot er co.n uucrations that the denflty of the earth nea. r t 11 e fiu r1ra ce fJ!Ould e 1ve tunes le [s th:ln 1ts mean dcnfit y. Phil. Tranf. Vol LXV 8 f h .n.· f 1 · • · P· 49 · But found rom t e attra~.:uon o t 1c moun tam Schehallien that it is prob bl h I . r a e, t e mean denfity of t1c earth 1s but double tiY<tt of the hill. IbiJ p e .., 2 H "f h fi (l . I] c • . J.) • ence I t e r fuppofitwn be we JOunded there would appear tube a cavity at the centre of conflderabl · d hfr om whence the immenfe beds · an.d .m ountains of lava ' to~" dflo b r. I e ma~mtu e, ne, a1a tes, gran1te, &c. ave been protruded. 8. The vanatwn of the compafs can only be accounted forb . fu pofing the central parts of the earth to con!ill of a fluid mafs anri th t f h "} ~. · h" . . • a part o t 1s flu 1d 1s tron, w 1ch requmng a greater degree of heat to bring it i-nt) fuflon tl 1 r. t 1 . r I'd d I . . . lang aJS or other m. e as, r'"e mams a w 1 , an . t 1e VIS mert1::e of this fl 11 id m.a fs w"' tl1 tl le ·li.O n ·I n J· t, occafions It to per1orm fewer revolutiOns than the crufl: of fo li c! earth ove "t 1 h · · d ll l f b I . r 1 , anc t us It 15 gr:t na y e t e tmcl, and the place where the floating iron refid · . · d - . I es IS po111te ·to by the dire :1:: or .r etrograde mottons of the magnetic needle . This fie ems to h ave b cen nearly tl. ... opm.ion.of Dr. H alley and Mr. Euler.· H! NOTE VII.-ELEMENTARY HEAT. Or.fphere o~ .fpbere in 7.vidming ·wrrves e.Ypand, And glad 7.Vilh ge11ial 7.oarmth /be incumbcut fa 11d. CANTO I. 1. J 43· A CERT ~IN q~1antity of hea t fcems to be combined with all bod ies befidcs the fenfible qu ant1ty wh1ch gravi tates like the elcCl:ric fluid amongfl: them Tl · l" 1 heat or latent heat of D Bl . ,. . us ccm >mec cr ft . ; . r. Jck, wh~n fet at 11berty by fermentation, inflamma tion , Y alltzat.on, freez1ng, or other chemtcal attractions producin cr new combination p:1 lfes ;.sl a ~utd element i~1to the furrouncling b ouies. A!1d by tluw~lg, cliffufion of ~cutral a ts 111 ~va ~e r, _m_el:mg, and other chemical jo!utions, a portion of hea t is at trafl.ecl from.. t.hc bodies U1 V1Clmty and enters into or become:; combined·wi th the new fulutions. |
