Observations of Underground Temperature. 127 



1. From depth 3 feet to 6 feet . . . '1250 



2. „ 6 „ 12 „ . . . -1163 



3. „ 12 „ 24 „ . . . -1128 



If now, in accordance with the proposed plan, we measure depths, 

 not in constant units of length, but in terms of thicknesses corre- 

 sponding to equal conducting powers and thermal capacities, 

 and if we continue to designate the thickness of the first stratum 

 by its number 3 of French feet, our reckoning for the positions 

 of the different thermometers will stand as follows : — 





Table VII. 



Thermometers 

 numbered 

 downwards. 



Depths in true 

 French feet 

 below No. I. 



Depths in terms of conductive 

 equivalents. 



II. 

 III. 



IV. 







3 



9 



21 





 3 



8-58+^gx 12 = 19-41 



According to this way of reckoning depths, we have the follow- 

 ing rates of variation of the logarithmic amplitudes, and of the 

 epochs separately, reduced from the previously stated means for 

 the whole period of eighteen years : — 



Table VIII. 



Rates of diminution 



of logarithmic am- 



Portions of rock. plitude per French 



foot, and conductive 



equivalents. 



Rate of retardation 



of epoch per French 



foot, and conductive 



equivalents. 



Between thermometers Nos. I. and II. 

 II. and III. 

 III. and IV. 



•1286 

 •1265 

 •1236 



•1215 

 •1236 

 •1264 



Between thermometers Nos. I. and IV. j -1252 



•1248 



28. Comparing this Table with the preceding Table VI., we 

 see that the discrepancies are very much diminished ; and we 

 cannot doubt that the conductive power of the rock is less in 

 the lower parts of the rock, and that the amount of the varia- 

 tion is approximately represented by Table VII. We have, how- 

 ever, in Table VIII. still too great discrepancies to allow us to 

 consider variation in the value of kc as the only appreciable de- 

 viation from Fourier's conditions of uniformity. 



29. In endeavouring to find whether these residual discre- 



