NOTES TO PRECEDING SECTION. 



119 



107 (p. 53.)— Here belonjj the admirable analytical la- 

 bours of Fourier, Uiot, Laplace, Poisson, Duhainel, and 

 Lam6. In his work.Thf'orie mafh6mati(iiie de la Chaleur, 

 1835, p. 3, 428—430, 436, and 521—524 (see also the 

 abstract of La Rive, in the Bibiiotheque universello de 

 Geneve, t. Ix. p. 415), Poisson has developed an hypoth- 

 esis totally different from the view advocated by Fou- 

 rier (Theorie. analyt. de la Chaleur). He denies the 

 present fluid state of the centre of the earth ; he believes 

 "that in cooling by radiation to the medium surrounding 

 the earth, the parts first consolidated on the surface sank 

 downwards, and that by a double upward and downward 

 current, the great inequality was lessened which would 

 have laken place in a solid body cooling from the surface." 

 The great geometrician thinks it more probable that the 

 consolidation commenced in the parts lying nearer to the 

 centre ; " the phenomenon of the increase of heat with the 

 depth does not extend to the whole mass of the earth, and 

 is a mere consequence of the motion of our planet in uni- 

 versal space, the several parts of which, by reason of their 

 stellar heat (chaleur stellaire) have very different tempera- 

 tures." The heat of the water of our Artesian wells, ac- 

 cording to Poisson, is therefore heat which has penetrated 

 the body of the earth from without ; the earth may be 

 viewed as we should a mass of rock transported from the 

 equator to the pole in so short a time, that it could not cool 

 completely. The increase of temperature in this block 

 would not extend completely to its centre. The physical 

 doubts which may reasonably be raised against this extraor- 

 dinary cosmical hypothesis, (an hypothesis which ascribes 

 to heavenly space what must much rather belong to matter 

 in its first transition from the gaseous to the solid state) 

 may he found collected in Poggendorff 's Annalea, Bd. xxxix. 

 6. 93- 1 (to. 



108 (p. 54.)— See above, pages 9, 15, and 16. The in- 

 crease in temperature is found in the Puits de Greneille 

 from 98'4 feet ; in the bore of New-Salzwerk, Minden, al- 

 most 91 feet ; at Pregny, Geneva, also 91 feel, although 

 there the outlet is 1510 feet al)ove the level of the sea. 

 This agreement of results, from bores that are severally 

 1683, 2094, and 680 feet in absolute depth, by a method first 

 suggested in 1821 by Arago, (Annuaire, 1835, p. 234) is 

 very striking. The two points of the earth at a short per- 

 pendicular distance from one another, whose annual tem- 

 perature is ascertained with the greatest precision, are 



frobably the external atmosphere of the Observatory of 

 'aris and of the cellar under the Observatory. The former 

 is 10O-822, the latter 110-834 C. ; difference 1O012 C. for 

 86 feet of depth (Poisson, Th6orie, &c., p. 415 and 462). 

 lu the course of the last 17 years, from causes which have 

 not been ascertained, the thermometer of the Caves has 

 risen 00-220 0. If the penetration of waters from lateral 

 channels into the main bore of Artesian wells produces some 

 disturbance, it must be admitted that in reference to mines 

 there are many more perturbing causes at work, and that 

 interfere with the accuracy of conclusions in reference to 

 their temperature at different depths. The general result 

 of Reich's great work on the temperature of the mines of 

 the Saxon Erzgebirge is the somewhat slow increase of 1° 

 C. for 128^ feet of descent. (Reich, Beob. iiber die Temper- 

 ature (les Gesteins in verschiedeneii Tiefen, 1834, S. 134.) 

 Yet Pliillips (Poggend. Ann. B. 34, S. 191), in a shaft of the 

 Monkwearmouth coal-pit, found an increase of 1° C. for 

 09-^^ feet of descent, exactly what Arago found in the Puits 

 de Greuelle. 



109 (p. 54.) — Bous-singault sur la Profondeur 4 laquelle 

 86 trouve la Couche de Temperature invariable entre les 

 tropiques, in the Anaales de Chimie et de Physique, t. liii. 

 1833, p. 225-247. 



110 (p. 55.)— Laplace, Exp. du Syst. du Monde, p. 229 and 

 263 ; Mecanique c61. t. v. p. 18 and 72, It is to be ob- 

 terved that the fraction ^ko ^^ * centigrade degree of a 

 mercurial thermometer, which is given in the text as the 

 limit of stability of the heat of the earth since Hippar- 

 chus's time, rests on the assumption that the dilatation of 

 the materials of which the body of the earth consists is the 

 same as that of glass = -^^L^^ for 1° C, of heat. Vide 

 on this point Arago, in Annuaire pour 1834, p. 177 — 190. 



111 (p. 55.)— William Gilbert of Colchester, whom Gal- 

 ileo calls " great to a degree that might excite envy," says, 

 '• Magnus magnes ipse est globus terrestris." He ridicules 

 the magnetic mountain of Fracastoro, the great contempo- 

 rary of Christopher Columbus, as the magnetic pole : " Re- 

 jicienda est vulgaris opinio de moiitibus magneticis, aut 

 rupe aliqua magnetica, aut polo phautastico a polo inundi 

 distanle." He assumes the variation of the magnetic needle 

 over the surface of the earth as unchanging: " Variatio 

 uniuscujusque loci constans est ;" and explains the isogenic 

 lines from the configuration o( continents and the relative 

 position of the sea basin, which has a weaker magnetic at- 

 tractive force than the solid masses that rise above the 

 ocean (Gilbert de Magnete, ed 1633, p. 42, «fcc.) 



112 (p. 55.)— Gauss, Allgemeine Theorie des Erdmag- 



nctismus, in den Resultaten aus den Beob. des magnet. 

 Vereins im Jahr. 1838, Ml, S. 56. 



113 (p. 55.)— There are also perturbations which do not 

 extend to any distance, which are more local, and perhaps 

 have their seat less deeply. A rare example of such extra- 

 ordinary perturbations, which aie felt in the Freiburg mines 

 and not in Berlin, was published by me now many years 

 ago (Lettre de M. de Humboldt k S. A. R. le Due de Sussex 

 sur les moyens propres i perfectionner la connaissance du 

 Magn6tismc terrestrc.in Becquerel'sTraite experimental de 

 I'Electricite, t. vii. p. 442). Magnetic storms that were ex- 

 perienced simultaneously from Sicily to Upsal, did not ex- 

 tend from Upsal to Altona (Gauss and Weber, Resullate 

 des magnet. Vereins, 1839, s. 128; Llovd, in the Comptes 

 rendus de I'Acadeinie des Sciences, t. x'iii. 1843, S6m. ii. p. 

 725 and 827). Among the many perturbations which in 

 recent times have been observed simultaneously over ex- 

 tensive districts of country, and which are collected in Sa- 

 bine's important work (Observ. on days of unusual magnetic 

 disturbance, 1843), one of the most remarkable is that of 

 the 25th September, 1841, which was noticed at Toronto in 

 Canada, at the Cape of Good Hope, at Prague, and partially 

 in Van Diemea's Land. The English Sunday, on which it 

 is sinful after Saturday night at 12 o'clock to read off a 

 scale, and to follow the grand phenomena of nature in their 

 course, intervening, broke off the observations in Van Die- 

 men's Land, and so made our information on this remarkable 

 storm incomplete ! 



114 (p. 55.) — The application of the magnetic inclination 

 to the determination of the latitude along a coast running 

 north and south, and which, like the shores of Chili and 

 Peru, is enveloped in fog (garua) for a portion of the year, 

 I published in Lam6therie's Journal de Physique, 1804, t. 

 lix. p. 449. The application in the locality indicated is the 

 more important, as, in consequence of the rapid current 

 from south to north as far as Cape Parisia, it occasions a 

 great loss of time to the shipping when the coast has to be 

 first approached northward from the destined port. In the 

 South Sea, from Callao de Lima harbour to Truxillo, with 

 a difference of 3° 57' of latitude, I have observed a variation 

 of the needle of 9° C. ; and from Callao to Guayaquil, with 

 a dirterence of 9° 50' of latitude, a variation of 2305O (vide 

 mv Relat. Hist. t. iii. p. 622). From Guarmey (10° 4' S. 

 lat.), Huaura (11° 3' S. lat.) to Chancay (IP 32' S. lat.), 

 the inclinations were 6-80°, 900O, and 10-35O. The deter- 

 mination of places by means of the magnetic inclination had 

 this remarkable feature about it, that where the ship's 

 course cuts the isoclinal lines almost perpendicularly, it is 

 the only one that is independent of all determination of 

 time, and so of the sight of the sun and other heavenly bod- 

 ies. I very lately, and for the first time, discovered propo- 

 sals to determine the latitude by the inclination of the 

 magnetic needle in Gilbert's work, De Magnete (lib. v. cap, 

 8, p. 200). This was scarcely 20 jears after the discovery 

 of magnetic inclination by Robert Norman. Gilbert even 

 points to the method as available *' aere caliginoso ;" and 

 Wright, in the preface which he has added to the great 

 work of his teacher, speaks of such a proposal as " worth 

 much gold." As he, with Gilbert, presumed erroneously 

 that the isoclinal magnetic lines ran parallel with the geo- 

 graphical circles of latitude, as also that the magnetic equa- 

 tor coincided with the geographical equinoctial line, he did 

 not perceive that the proposed method was only capable of 

 a local and much more limited application than that he im- 

 agined. 



115 (p. 55.) — Gauss and Weber, Resultate des magnet- 

 ischen Vereins in J. 1838, ^ 31, s. 46. 



116 (p 55.)— According to Faraday (Loudon and Edin- 

 burgh Philosophical .Magazine, 1836, vol. viii. p. 178), pure 

 cobalt is totally without magnetic power. Rose and Wohl- 

 er, again, do not admit this as absolutely ascertained. If 

 one of two masses of cobalt (both of which are believed to 

 be pure) shows itself totally indifferent to magnetism, it 

 seems to me likely that the other which shows magnetic 

 properties does so in virtue of some impurity. 



117 (p. 55.) — Arago, in the Annales de Chimie, torn, xixii. 

 p. 214 ; Brewster, Treatise on Magnetism, 1837, p. Ill ; 

 Baumgartner, in the Zeitschrift fiir Phys. und Mathem. 

 Bd. ii. s. 419. 



118 (p. 55.)— Humboldt, Examen critique de I'hist. de la 

 Geographic, tom. iii. p. 36. 



119 (p. 55.) — Asie centrale, tom. i. Introduction, p. 

 xxxvii— xlii. The western nations, the Greeks and the Ro- 

 mans, knew that magnetism could be communicated for a 

 great length of time to iron ("sola haec materia ferri vires 

 a. magnete lapide accipit retinetque longo tempore " Plin. 

 xxxiv. 14). The great discovery of the terrestrial directive 

 force therefore depended alone on this, that no one in the 

 west happened to observe a longish piece of magnetic iron 

 ore or a magnetized iron rod, floated at liberty upon water 

 by means of a piece of wood, or balanced and suspended 

 freely in the air by means of a thread. 



120 (p. J56.) — A very slow secular progression or a local 

 invariability of the magnetic declination may be of great 



