204 REPORT— 1876. 



Ninth Report of the Committee, consisting of Pi'of. Everett, Sir W. 

 Thomson, F.R.S., Prof. J. Clerk Maxwell, F.R.S., G. J. Symons, 

 F.M.S., Prof. Ramsay, F.R.S., Prof. A. Geikie, F.R.S., James 

 Glaisher, F.R.S., George Maw, F.G.S., W, Pengelly, F.R.S., 

 Prof. Hull, F.R.S., Prof. Ansted, F.R.S., Prof. Prestwich, 

 F.R.S., Dr. C. Le Neve Foster, Prof. A. S. Herschel, G. A. 

 Lebour, F.G.S., and A. B. Wynne, appointed for the purpose of 

 investigating the Rate of Increase of Underground Temperature 

 downwards in various Localities of Dry Land and under Water. 

 Drawn up by Prof. Everett, Secretary. 



A remarkable series of observations have recently been taken in a boring 

 at Sperenbcrg, near Berlin. The bore was carried to the depth of 4052 

 Rhenish (or 4172 English) feet, and was entirely in rock-salt, with the excep- 

 tion of the first 283 feet, which were in gypsum with some anhydrite. Tlie 

 observations were taken under the direction of Herr Eduard Danker, of 

 Halle an der Saale, and are described by him in a paper occupying thirty- 

 two closely printed quarto pages (206-238) of the 'Zeitschrift fiir Berg-, 

 Hiitten- und Salinen-AVesen ' (xx. Band, 2 and 3 Lieferung : Berliu, 1872), 



The instrument employed for measuring the temperatures was the earth- 

 thermometer of Magnus, which gives its indications by the overflowing of 

 mercury, which takes place when the instrument is exposed to a higher tem- 

 perature than that at which it was set. To take the reading, it is immersed 

 in water a little colder than the temperature to be measured ; the tempera- 

 ture of this water is noted by means of a normal thermometer, and at the 

 same time the number of degrees that are empty in the earth-thermometer is 

 noted. From these data the maximum temperature to which the instrument 

 has been exposed can be deduced, subject to a correction for pressure, which 

 is not very large, because the same pressure acts upon the interior as upon 

 the exterior of the thermometer. 



In the following resume (as in the original paper) temperatures are ex- 

 pressed in the Reaumur scale, and depths in Rhenish feet, the Rhenish foot 

 being 1-029722 English foot. 



Observations were first taken, at intervals not exceeding 100 feet, from the 

 depth of 100 feet to that of 4042 feet, the temperature observed at the former 

 depth being 11°, and at the latter 38°-5 ; but all these observations, though 

 forming in themselves a smooth series, were afterwards rejected, on the 

 ground that they were vitiated by circulation of water and consequent con- 

 vection of heat. 



It has often been supposed that though this source of error maj' affect the 

 middle and upper parts of a bore, it cannot aflect the bottom ; but the Speren- 

 berg observations seem to prove that no such exemption exists. When the 

 bore had attained a depth of nearly 3390 feet, with a diameter of 12 inches 

 2 lines at the bottom, an advance-bore of only 6 inches diameter was driven 

 17^ feet further. A thermometer was then lowered halfway down this 

 advance-bore, and a plug was driven into the mouth of the advance-bore so 

 as to isolate the water contained in it from the rest of the water above. After 

 twenty-eight hours the plug was drawn and the thermometer showed a tem- 

 perature of 36°-6. On the following day the temperature was observed at the 

 same depth without a plug, and found to be 33°- 6. Another observation with 

 the plug was then taken, the thermometer (a fresh instrument) being left 

 twenty-four hours in its position. It registered 36°-5, and again, without 



