On the Bate of Increase of Underground Temperatures. 453 



water a little colder than the temperature to be measured ; the 

 temperature of this water is noted by means of a normal ther- 

 mometer, 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) tempera- 

 tures are expressed in the Eeaumur scale, and depths in 

 Rhenish feet, the Ehenish foot being 1-029722 English foot. 

 Observations were first taken at intervals not exceeding one 

 feet, from the depth of one hundred feet to that of 

 4042 feet, the temperature observed at the former depth being 

 ll'O, and at the latter 38"5 ; but all these observations, though 

 forming in themselves a smooth series, were afterward rejected, 

 on the ground that they were vitiated by circulation of water 

 and consequent convection of heat. 



It has often been supposed that though this source of error 

 may affect the middle and upper parts of a bore, it cannot 

 affect the bottom ; but the Sperenberg observations seem to 

 prove that no such exemption exists. When the bore had 

 attained a depth o( nearly 3.390 feet, with a diameter of twelve 

 inches two lines at the bottom, an advance bore of onlv six 

 inches diameter was driven seventeen and one-half feet further. 

 A thermometer was then lowered half-way down this advance 

 bore, and. a plug was driven into the mouth of this 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 temperature of 86'6. 

 On the following day the temperature was observed at the 

 same depth without a plug, and found to be 33'6. Another 

 plug was then taken, the thermometer (a 

 fresh instrument) being left twenty-four hours in its position. 

 It registered .V. .". i !._ • . vi: • r • ,_-_ - -rave on the 

 same day 33-9. It thus appears that the effect of convection 

 was to render the temperature in the advance bore 3° E. too 



Apparatus was then employed for isolating any portion of a 

 bore by means of two plugs at ; art with 



the thermometer between them. This operation was found 

 much more difficult than that above described, but m several 

 instances it gave results which were deemed 

 while in other instances the apparatus broke, or the plugging 

 was found imperfect. The deepest of the successful observa- 

 tions by this method was at 2,100 feet, and the shallowest was 

 at 700 feet The first 444 feet of the bore were lined with iron 

 Am. Joub. Scl-Third Series, Vol. XIII, No. 7S.-Jcne, 1877. 



