of Edinburgh^ Session 186'3-64. 201 
of conductivity founded on the gramme-water-second-centimetre 
units, is '005. Taking this, therefore, as an average conductivity 
in the earth’s upper crust, we find that if the temperature in“ 
creased downwards at the rate of 1 ° per 20 centimetres, the 
quantity of heat lost by conduction outwards would be 40 V 5 
therefore, according to Peclet’s result, this would keep the surface 
just 1 ° warmer than it would be if there were no conduction of 
heat from within. Hence, to warm the surface to 10° Fahr. above 
what it would be if there were no conduction from within, the rate 
of rise of temperature must be 1° Fahr. per 2 centimetres, or -0656 
of a foot (which would probably destroy the roots of any large tree 
or plant), but at all events could not, as I have shown,* be the real 
condition of the earth at any time later than about 180 years after 
even a greater heating (7000° Fahr.) of the whole globe than the 
greatest we can suppose it at all probable the earth ever ex- 
perienced. Hence it is certain that the climate can never have 
been sensibly influenced from the earliest “geological” era by 
underground heat. This conclusion was stated in § 17 of the 
paper already referred to “On the Secular Cooling of the Earth,” 
as rendered certain by a rough general knowledge of the circum- 
stances, without any approach to an accurate estimate of the ab- 
solute amount of radiation. 
We now see, farther, that the present rate of underground rise 
of temperature, estimated at 1° Fahr. per 50 feet, is only yL-th of 
that which is required to warm the surface by 1 °. Hence the 
surface is only about f^th. of 1° Fahr. warmer at present than it 
would be if there were no supply of heat from within. 
The following Donations to the Library were announced:— 
The Canadian Journal of Industry, Science and Art. No. 49, 8 vo. 
— From the Canadian Institute. 
De rOrigine des lacs Suisses, par M. B. Studer. 8 vo . — From the 
Author. 
Proceedings of the Koyal G-eographical Society. Vol. YIII. No. 
2. 8 vo . — From the Society. 
* Traus. R.S.E., April 1862, “ On the Seciflar Cooling of the Earth,” § 18. 
