250 



ON UNDERGROUND TEMPERATURE. 



feet.) At this place the following mean temperatures and epochs of 

 maxima have been obtained : 



At Edinburgh the following results were obtained 



For the greatest depth, the time required for the heat-wave to reach 

 it is nearly sis months, making the snrface maximum temperature co- 

 incident with the minimum temperature of the stratum, 7.32 meters 

 below. 



In the case of Chicago, we may take the mean annual temperature of 

 the atmosphere just above the surface=8o.l7 C. ; that of the surface of 

 the soil = 80.0 C. The increase for a depth of 12.2 meters lor the lowest 

 stratum of clay and to the rock-surface will be 0^.44 C, making 80.44 0. 

 for this depth. The invariable temperature may be estimated about 9 or 

 10 C, and may be found at a depth between 30 and 40 meters, the 

 variations being transmitted to a greater depth in rock than in clay. 

 At the surface of the rock the variations of temperature will probably 

 yet amount to 0°.!, (according to the Edinburgh observations.) For a 

 depth of 229 meters, corresponding to the depth from which the well- 

 water flows, the increase of heat should amount to 8o.2 C, according to 

 the mean given above; hence the computed temperature 16o.2 0. But 

 the observed temperature is only 120.8 C, showing either a much slower 

 rate of increase (1° C. in 48 meters) or a local deviation, probably due 

 to infiltration of water from a higher level. Whether the lake-water, 

 which is colder at the same depth than solid matter would be, can 

 exert an influence by conduction, I do not know. 



Prof. J. D. Everett, chairman of the committee of the British Asso- 

 ciation for the Advancement of Science, on the subject of underground 

 temperature has published a number of valuable reports The follow- 

 ing is an extract from a recent communication of his to the Belfast 

 Natural History and Philosophical Society : 



" The phenomena of underground temperature may conveniently be 

 classed under two heads, according as attention is directed to the tirst 

 forty or fifty feet, or to such depths as are attained in mines and artesian 

 wells. 



