1902 - 3 .] Mr G. Romanes on Cause of Earth's Internal Heat. 419' 
The outflow of molten lava from a volcano is not a proof that 
the rock from which the lava was formed had as high a tempera- 
ture as the lava, because in escaping from under a vertical pressure 
of some miles of rock much energy must have been converted into 
the form of heat in squeezing the more or less plastic rock into the 
fissure which formed the vent of the volcano. 
As yet we have not considered the effect of an extensive 
atmosphere in accelerating the final aggregation of the earth’s 
mass, and consequently in raising the temperature of the surface- 
portions. 
As the small masses of matter, which we have supposed to have 
originally constituted the nebulous ring from which the earth was 
formed, could not have held any gas by gravitation, the atmosphere, 
and probably the ocean also, must have been formed from matter 
either chemically combined in or occluded in the pores of these 
nebulous masses, and the heat of collisions was probably the cause 
of the liberation of the gases from which the atmosphere and 
probably the ocean also was formed. An atmosphere so formed 
round the growing earth indicates intense heat to cause its 
formation, but probably not intense heat of the whole at the 
same time, as it would be developed very gradually. It would 
retard and soon bring to the surface all matter that grazed it, and 1 
so cause a more rapid development of heat and retain it longer 
than would be the case with a small body like the moon, which 
appears not to be able to retain any gas on its surface by reason of 
its comparatively feeble gravitating influence. To trace all the 
effects of an atmosphere in this way is quite beyond the writer’s 
power, but he thinks there would be a time when the atmosphere 
contained an immense amount of water vapour, in consequence of 
the surface heat, and in proportion as this was the case storms and 
geological action of all kinds would be correspondingly energetic. 
He thinks also that although volcanic * action must have had great 
influence on the gradient of temperature near the surface in many 
places, yet gradual gravitational contraction of the mass has been 
the chief cause in determining this gradient, because the heat so 
developed was greatest nearest the centre, and consequently must 
* Perhaps volcanic action should he considered as a manifestation of 
gravitational contraction. 
