38 



IlEPORT — 1889. 



tions at the 58 different depths; the second column contains the depths 

 in metres ; and the tliird column, the temperatures observed at these 

 depths in isolated water-columns. The fourth column contains the excess 

 of the temperature so observed above the temperature observed by means 

 of the secondary thermometer in the free water just above the plug. 

 The fifth column contains the differences between the successive numbers 

 in the third column — in other words, the increase of temperature for 

 each 30 m. of depth. 



The smallness of the effect of isolation, as shown, in the fourth column 

 of the Table, is very noteworthy, its greatest value being 1° R., and its 

 average value about ^ of 1° R. At Sperenberg it amounted in several 

 cases to about 3" R. The smallness of the effect in the present case 

 is attributable to the narrowness of the bore, which tells in two ways : 

 there is more frictional resistance to the movement of the water ; and the 

 thermal capacity of a given length of column is less in comparison with 

 its surface of contact with the sides of the bore. 



As a further experiment on the prevention of convection, a wooden 

 plug was driven into the bore at the depth of 438 m., thick mud was 

 introduced till it filled all the bore above this plug, and observations 

 were taken with a maximum thermometer in the mud at depths from 

 426 ni. to 126 m. A second plug was then driven in at the top of the 

 tubing, which was 120 m. beneath the surface of the ground, and the 

 observations were continued upwards from 118 m. to 6 m. The observa- 

 tions thus taken in the mud are given in the second column of Table II. 

 They are rather higher than those previously obtained at the same depths, 

 which are repeated from Table I. for comparison, the greatest difference 

 occurring at the depth of 276 m., where it amounts to 0°"9 R. Herr 

 Dunker suggests that the difference may have arisen from insufficient 

 time being allowed for the muJ to take the permanent temperature. 



Table IT. 



