38 Interior Condition of the Earth. — Le Conte. 
ments was not fashioned from materials of this terrestrial 
globe but had come to them from the unknown regions of 
space. Their iron was, in fact of meteoric origin, like that of 
the Mayas of Yucatan and the Incas of Peru of which many 
weapons are still preserved in collections. 
{Continued.) 
THE GENERAL INTERIOR CONDITION OF THE EARTH.> 
By Joseph Le Conte. 
It is well known that the interior temperature of the earth 
increases at the average rate of 1° for every 50-60 feet of depth. 
For convenience we will take it at 1° for every 52.8 feet, or 
100° per mile. At this rate at the depth of 25 miles we should 
reach a temperature at which all ordinary rocks would melt. 
The older geologists therefore assumed that the earth is an 
incandescent liquid globe beneath a comparatively thin solid 
crust . 
But physicists now tell us that this is impossible. Thom- 
son and Darwin^ have conclusively shown that in all its 
cosmic relations, and especially under the tide-generating in- 
fluences of the sun and moon, the earth behaves not like a sub- 
stantially liquid, but like a substantially solid and very rigid 
body .; that in fact it is, as a whole, more rigid than a globe of 
glass and even as rigid as a solid globe of steel of the sfeme 
size. 
An outline of the physical argument may be briefly put as 
follows : Suppose, 1st, the earth to be a liquid globe of mercury 
revolving as now under the moon. Evidently a tide affecting 
the whole mass (earth tide), would follow the moon. Suppose, 
2nd, such an earth covered two miles deep with a universal 
ocean. In this case there would be a tide affecting the whole 
compound mass ; but the water-tide, upon the mercury-tide, 
being but ^^5^ of the whole would be imperceptible. Sup- 
pose, 3rd, a liquid globe covered by a solid shell 25 miles 
^This paper was given as a lecture before the California Academy 
of Science, May 7th, 1888. Having delayed publication, and an ad- 
mirable paper on the same subject and reaching similar conclusions by 
Prof. Claypole having in the meantime appeared in the June and 
July numbers of this magazine, I gave up the idea of publishing at all. 
But I find the mode of presentation so different that on second thought 
I still believe the paper may be useful at least to teachers of geology. 
^ Nature, vol. 27. p. 22, 1882; vol. 14, p. 426,1876. Thomson and 
Tait, Natural Philosophy. 
