158 COSM )i5. 



do not extend beyond a vertical depth of somewhat more than 

 2000 feet (about one third of a geographical mile) below the 



point) and the relative depth (or that beneath the level of the sea). The 

 greatest relative depth that man has hitherto reached is probably the 

 bore at the new salt-w^orks at Minden, in Prussia: in June, 1814, it 

 was exactly 1993 feet, the absolute depth being 2231 feet. The tem 

 perature of the water at the bottom was 91° F., which, assuming the 

 mean temperature oi' the air at 49° -3, gives an augmentation of tera- 

 peratui-e of 1° for every 54 feet. The absolute depth of the Artesian 

 well of Crenelle, near Paris, is only 1795 feet. According to the ac- 

 count of the missionary Imbert, the fire-springs, " Ho-tsing," of the Chi- 

 nese, which are sunk to obtain [carbureted] hydrogen gas for salt-boil- 

 ing, far exceed o'lr Artesian springs in depth. In the Chinese province 

 of Szii-tschuan these fire-springs are very commonly of the depth of 

 more than 2000 feet; indeed, at Tseu-lieu-tsing (the place of continual 

 flowj there is a Ho-tsing which, in the year 1812, was found to be 3197 

 feet deep, (tliimboldt, Asie Centrale, t. ii., p. 521 and 525. Annates 

 de V Associatini dc la Propagation de la Foi, 1829, No. 16, p. 369.) 



The relati re depth reached at Mount Massi, in Tuscany, south of 

 Volterra, amounts, according to Matteuci, to only 1253 feet. The bor- 

 ing at the new salt-works near Minden is probably of about the same 

 relative depth as the coal-mine at Apendale, near Newcastle-under 

 Lyme, in Staftbrdshire, where men vvork 725 yards below the surface 

 of the earth. (Thomas Smith, iV/iner's Gwiie, 1836, p. 160.) Unfortu- 

 nately, I do not know the exact height of its mouth above the level 

 of the sea. The relative depth of the Monk-wearmouth mine, near 

 Newcastle, is only 1496 feet. (Phillips, in the Philos. Mag., vol. v., 

 1834, p. 446.) That of the Liege coal-mine, V Espirance, at Seraing, 

 is 1355 feet, according to M. von Dechen, the director; and the old 

 mine of Marihaye, near Val-St. -Lambert, in the valley of the Maes, 

 is, according to M. Gernaert, Ingenieur des Mines, 1233 feet in depth. 

 The works of greatest absolute depth that have ever been formed 

 are for the most part situated in such elevated plains or valleys that 

 they either do not descend so low as the level of the sea, or at most 

 reach veiy little below it. Thus the Eselschacht, at Kuttenberg, in Bo- 

 hemia, a mine which cau not now be worked, had the enormous abso- 

 lute depth of 3778 feet. (Fr. A. Schmidt, Berggeseize der oster Man., 

 abth. i., bd. i., s. xxxii.) Also, at St. Daniel and at Geish, on the Rorer- 

 b(ihel, in the Landgericht (or provincial district) of Kitzbiihl, there 

 were, in the sixteenth century, excavations of 3107 feet. The planf 

 of the works of the Rorerbtihel are still pi-eserved. (See Joseph von 

 Sperges. Tyroler Bergwerksgeschichte, s. 121. Compare, also, Hum- 

 boldt, Oiitachten uber H erantreibung des Meissner Siollens in die Frei' 

 berger Erzrevier, printed in Herdei', uber den jelz begonnenen Erbstol- 

 len, 1838, s. cxxiv.) We may presume that the knowledge of the ex- 

 traordinary deptli of the Rorerbtihel reached England at an early period, 

 tor I find it remarked in Gilbert, de Magnete, that men have penetrated 

 2400 or even 3000 feet into the crust of the Earth. (" Exigua videtur 

 terrae portio, quae unquara hominibus spectanda emerget aut eruitur* 

 cum profundiusin ejus viscera, ultra .^florescentis extremitatis corrupte- 

 iam. aut propter aquas iu magnis fodin. tanquam per venas scatu rientes 

 ttut propter aeris salubrioi'is ad vitam o erariorum sustinendam neces- 

 garii defectum, aut propter ingentes sumi^tus ad tantos labores *xant- 

 landos multasqu^ difBcultates. ad profundi wes terrte partes penetrar« 



