ON THE KATE OF INCREASE OF UNDERGKODND TEJirEBATDRE. 35 



Eighteenth Report of the Committee, consistinrj of Professor Everett, 

 Professor Sir William Thomson, Mr. Gr. J. Symons, Sir A. C. 

 Ramsay, Dr. A. Geikie, Mr. J. Glaisher, Mr. Pengelly, Pro- 

 fessor Edward Hull, Professor Prestwich, Dr. C. Le Neve 

 Foster, Professor A. S. Herschel, Professor G. A. Lebour, Mr. 

 A. B. Wynne, Mr. Galloway, Mr. Joseph Dickinson, Mr. G. F. 

 Deacon, Mr. E. Wethered, and Mr. A. Strahan, appointed for 

 the purpose of investigating the Rate of Increase of Under- 

 ground Temperature dowmvards in various Localities of Dry 

 Land and under Water. {Draiun up by Professor Everett, 

 Secretary.) 



Very important observations have been publisbed ' during the past 

 year by Herr Dnnker, whose observations in a very deep bore at Speren- 

 berg were embodied in our Report for 1876. The new observations were 

 taken at Schladebach, near Diirrenberg, in a bore of greater depth and 

 smaller diameter than that at Sperenberg, and with similar precautions 

 against convection currents. The depth was 1,748 metres, the bore 

 passing through new red sandstone (Buntsandstein), maguesian lime- 

 stone (Zechstein), lower Permian sandstone (Rothliegendes), and coal- 

 measures (Steiukohlengebirge), to the upper Devonian beds (Oberdevon). 



It was tubed to the depth of 1,240 metres. For the first 584 metres 

 the diameter was 120 millimetres ; for the next 104 m. it was 92 mm. ; 

 then for 393 m.. it was 72 mm., and for the next 159 m. it was 50 mm. 

 From this point to the bottom the diameter gradually diminished to that 

 of a man's little finger. The diamond borer was the instrument employed 

 in sinking it. 



Indiarubber bags, such as were used at Sperenberg for preventing 

 convection currents, being deemed imsuitable for such a narrow bore, a 

 plugging of moist clay was employed, constructed as follows : — 



On a cylindrical rod, which might be of tough wood for bores of 

 moderate depth, but was of iron in the actual observations, are two 

 wooden discs of such size that there is only just room for them to move 

 in the bore. The lower disc is fixed, and tlie upper movable on the rod. 

 The part of the rod below the fixed disc has a length equal to that of the 

 water-column which it is desired to isolate. The maximum thermometer 

 with wliich the temperatures are taken has its bulb half way down this 

 portion of the rod. It is fastened beside the rod if thei-e is room for it ; 

 and when the bore is too narrow for this arrangement, the thermometer 

 is placed in a metal box which may be described as forming part of the 

 rod, the rod being divided into two portions screwed to the two ends of 

 the box. The movable disc is removed to a measured distance from the 

 fixed one, and the space between them is then filled with clay which has 

 been made plastic by kneading it with water, so that it forms a cylinder 

 with the two discs. 



When the pole presses on the bottom of the bore, part of the weight 

 of the boring rods is supported on the upper disc, thus squeezing the 

 clay against the sides of the bore and forming a water-tight plug. 



' J\^aie» JahrhtchfUr Mineraloglc, &c , 1889, B<3. 1. 



D 2 



