340 Address of Sir Wm. Thomson at the Glasgow Meeting. 
perature, there is generally found a gradual increase of tempera- 
ture downward, approximating roughly, in ordinary localities, 
to an average rate of 1° C. per thirty meters of descent, but 
much greater in the neighborhood of active volcanoes, and cer- 
tain other special localities of comparatively small area, where 
hot springs and, perhaps, also, sulphurous vapors prove an 
intimate relationship to volcanic quality. It is worthy of 
remark in passing, that, so far as we know at present, there are 
no localities of exceptionally small rate of augmentation of 
underground temperature, and none where temperature dimin- 
ishes at any time through any considerable depth downward 
below the stratum sensibly influenced by summer heat and 
would be sensibly reached at a depth of 600 meters. 
By a simple effort of geological calculus it has been estimated 
that 1° per 30 meters gives 1000° per 30,000 meters, and 3333 
per 100 kilometers. This arithmetical result is irrefragable, 
but what of the physical conclusion drawn from it with mar 
vellous frequency and pertinacity that at depths of from 30 to 
100 kilometers the temperatures are so high as to melt all sub- 
stances composing the earth’s upper crust? It has beep 
remarked, indeed, that if observation showed an diminution 
or augmentation of the rate of increase of undergroud tempera 
ture in great depths, it would not be right to reckon on the 
uniform rate of 1° per 30 meters, or thereabouts, down to 30 oF 
60 or 100 kilometers. ‘But observation has shown nothing of 
temperature downward were found at a depth of one he 
this would demonstrate* that within the last 100,000 years 
eat I 
* For proof of this and following statements regarding Underground H 
refer to “Secular Cooling of Heng ,” Transactions of the Royal Society 
Edinburgh, 1862, and Thomson and Tait’s “Natural Philosophy,” APPe™ 
