III.—On the Rate of Increase of Underground Temperature

Extract

In the 22nd Report of the Committee appointed to investigate the rate of increase of underground temperature, read this year before the British Association in Glasgow, some remarks previously made by me are animadverted upon; and as the Secretary, Professor Everett, has invited me to discuss the matter with him, I take the opportunity of entering somewhat more fully into the question of conductivity than has hitherto seemed necessary. We read in the Report “… . in view of the fact that the President of Section C last year characterised the variation in the British Isles ‘from 1° in 34 feet to 1° in 92 feet’ as ‘a surprising divergence of extremes from the mean,’ it is well to emphasise the connection between gradient and conductivity. If there is anything like uniformity in the annual escape of heat from the earth at different places, there must necessarily be large differences in geothermic gradients, since the rate of escape is jointly proportional to the gradient and the conductivity.”