CORRELATION OF ISOGEOTHERMAL SURFACES 47 
TABLE III. Mean values of a, b, and 1/b. 
100-1000 feet 100-2000 feet 
No. No. 
of a r To b r X 10579108 1/6 | of b r X 10579105) 1/b 
Obs. Obs. 
5 | 72.8 | 1.2 | 0.5 |0.01781 58 26 56.1 5 0.01776 44 20 56.3 
35 | 71.3 | 1.4 | 0.2 | .01885 9 2 53.0 | 35 | .01878 59 10 53.2 
10 | 73.4} 1.6 | 0.5 |0.01804 87 28 55.4 | 10 |0.01804 63 20 55.4 
30 | 70.9} 1.0 | 0.2 | .01895 88 16 52.8 | 30 | .01885 55 10 53.0 
10 |} 73.4 | 1.6 | 0.5 |0.01804 87 28 55.4 | 10 |0.01804 63 20 55.4 
10 |} 70.9; 1.0 | 0.3 | .01919 81 26 52.1 9 | .01923 34 11 52.0 
10 | 71.2 | 1.1 | 0.3 | .01855 | 108 34 53.9 | 10 | .01849 69 22 54.1 
10 | 70.4 | 1.1 | 0.3 | .01912 74 23 5253 9 | .01882 38 13 53.1 
source of error, Table III has been computed. The table is based on the data 
from 40 wells, two of the poorest values being omitted. In the first two lines, 
the mean values for 5 wells highest on the structure are compared with the 
means from the remaining 35 wells. Similarly, in the third and fourth lines, 
the means for 10 wells highest on the structure are compared with the means 
from the remaining 30 wells, while in the final tabulation the wells have been 
grouped in four successive groups as regards elevation on structure, the first 
TABLE IV. Gradients and reciprocal gradients (H =360 feet; and H=320 feet). 



In air on slope Beneath adjacent Beneath summit 
of hill plain of hill 
Gradients Reciprocal Gradients Reciprocal 
(a’) gradients (a) gradients 



0.00028 27 




0.00006 | 303.8} 166.7] 0.00030} 60.8} 33.3 | 0.00023 81 42.0 
0.00005 | 364.5 | 200.0} 0.00036 | 50.6 | 27.8] 0.00028 01 35.7 
0.00005 | 364.5 | 200.0) 0.00030} 60.8} 33.3 | 0.00023 56 42.5 
0.00006 | 303.8 | 166.7 | 0.00036 | 50.6} 27.8] 0.00028 64 34.9 
0.00006 | 303.8] 166.7} 0.00030 | 60.8] 33.3 | 0.00024 11 41.5 
0.00005 | 364.5 | 200.0] 0.00036 | 50.6] 27.8} 0.00028 40 35.2 
0.00005 | 364.5 | 200.0 | 0.00030 | 60.8 | 33.3 | 0.00023 87 41.9 



group as heretofore being the highest. The table shows clearly that the values 
of a and 1/0 in the first group of each set are always the highest. However, 
minor irregularities of this kind can not always be attributed to pumping 
operations. In general, the depth-temperature curves become more irregular 
as the surface of the ground is approached. It is for this reason that a map 
showing the isothermal surfaces is much more reliable than a map showing 
the distribution of reciprocal gradients. In addition to the preceding irregu- 
larities, the variation of the annual mean temperature of the air over the 
191 
