1870.] ( 207 ) 



V. KECENT OBSEEVATIONS ON UNDERGROUND TEM- 

 PERATURE, OR THE CAUSES OF VARIATION IN 

 DIFFERENT LOCALITIES. By Edward Hull, M.A., 

 F.R.S., Director of the Geological Survey of Ireland. 



Within the last year several series of experiments on the rate of 

 increase of underground temperature of more than ordinary interest 

 have been carried out, on which I propose to offer a few observa- 

 tions. On a former occasion I ventured to give a summary of the 

 experiments which had at that time been carried out on this inte- 

 resting branch of inquiry, and to point out a course which, in my 

 opinion, would if adopted enable us to ascertain the rate of increase 

 at depths hitherto unexplored.* It is satisfactory to find that the 

 plan proposed has met with the approval of the Committee appointed 

 by the British Association for the Advancement of Science, for the 

 purpose of " investigating the rate of increase of underground tem- 

 perature downwards in various localities." The report for the past 

 year, drawn up by Professor Everett at the request of his colleagues, 

 has now been issued, and contains an account of experiments under- 

 taken by Sir William Thomson, F.R.S., and his assistant, Mr. 

 McFarlane, in the vicinity of Glasgow, and by Mr. G. J. Symons at 

 Kentish Town in the metropolis, at the deep boring of the New 

 River Company. These observations were taken in water which 

 filled the bore-holes, each layer or stratum of water being assumed 

 to correspond in temperature with that of the surrounding stratum 

 of rock ; and the instruments used were those invented by Sir W. 

 Thomson and Professor Phillips respectively for avoiding a source of 

 error (though one not of much importance) arising from the pressure 

 of the water at considerable depths on the bulb of the thermometer. 

 Of the two experiments made near Glasgow: one, taken at 

 Blythswood reached a depth of 525 feet, with an ultimate tempera- 

 ture of 59*52° ;f an( l the other, taken at South Balgray, reached a 

 depth of 347 feet, with a temperature of 53*69°. At a depth of about 

 60 feet the constant temperature was reached, and the result obtained 

 at the Blythswood bore was 1° for every 50*5 feet, and at the South 

 Balgray bore 1° for every 41 feet, a rate of increase much in excess 

 of the former ; and, I may add, of the mean results of other experi- 

 ments.:!: 



* ' Quart. Journal of Science,' vol. v. 1868. 



t All measurements of temperature in this paper are given in degrees of 

 Fahrenheit. 



+ The rapid increase in this case appears to have arisen from the large pro- 

 portion of shale at the depth between 390 and 450 feet. Mr. W. Hopkins has 

 shown that the increase of temperature is in the inverse ratio of the thermal 

 conductivity. ' Phil. Trans.,' vol. cxlvii. 



