1876.] upon the Distribution of Heat in a Borehole. 



15 



was argued that this agrees with the result that might be ex- 

 pected; and that the temperature curve corresponding to this 

 effect would tend to a parabolic form. 



For suppose OA to represent the temperature at the surface ; 

 AC the temperature curve within the body of the rock, the 



^ n 



n \C 



ordinate increasing proportionally to the depth. If there were no 

 convection currents, AG would be likewise the curve of tem- 

 perature of the water in the borehole. Next, suppose that there 

 are convection currents ; but that no heat is radiated away from 

 the surface of the water : then the currents, warming the upper 

 portion of the column of water and cooling the lower, will cause 

 its curve of temperature to deviate from AGirv some such manner 

 as does BE, intersecting AG. But at the surface of the water in 

 a large borehole (in the present case a foot across) the temperature 

 would be reduced nearly to that of the atmosphere by radiation 

 and evaporation ; so that the interval AD would almost disappear, 

 and the temperature curve be drawn towards OM, but more so in 

 the upper than in the lower part. Thus it would assume a some- 

 what parabolic form, intersecting the temperature curve of the 

 rock at no great distance from the surface. 



Dunker seems to have taken the difference of temperature 

 when the currents were interrupted and when they were not so, 

 as indicating the difference of temperature between the water and 

 the rock mass. But, in order to obtain the true rock temperature 

 by interrupting the currents, it would have been necessary to 

 have kept the thermometer down in the included water for a 

 much longer period than was done, because when the rock tempe- 

 rature had, by long exposure to the action of the currents, been 

 reduced below its true temperature for a considerable distance in 

 laterally from the borehole, it would take a long while to recover 

 itself. An instance was cited from the well at La Chapelle, Paris, 



