1902-3.] Mr G. Romanes on Cause of Earth's Internal Heat. 415 
Suggestion as to the Cause of the Barth’s Internal 
Heat. By George Romanes, C.E. Communicated by 
Dr C. G. Knott. (With a Plate.) 
(Read January 5, 1903.) 
During the discussions that have arisen as to the internal heat 
of the earth, the writer has never seen any reason given for 
supposing that there was a time when the earth was a highly 
heated fluid mass, and he believes that view to have originated by 
analogy from the case of the sun ; and no other cause of the heat 
seems to be generally assumed than the collisions of the parts that 
came together to form the earth’s mass. He has expected to find 
some one maintaining that gradual gravitational compression of the 
mass was the main source of the earth’s internal heat, but till 
recently he has never tried to find out if it could possibly be a 
sufficient cause. It has always seemed to him that the formation 
of the earth’s mass must have been accomplished under circum- 
stances so different from the case of the sun that an analogy could 
scarcely be drawn between the two cases ; indeed, it is obvious that 
the amount of heat produced by the formation of planets from 
nebulae will depend principally on their masses, and will be in a 
higher ratio than that of the masses. 
The earth must have drawn its substance, with extreme slowness, 
from a wide ring of nebulous matter circulating round the sun, of 
which its orbit would be a nearly central line ; and if we may 
suppose all, or nearly all, of this matter circulating in the same 
direction, there would be few sufficiently violent collisions to 
liquefy the matter, until the masses, into which this ring of matter 
would tend to collect, were so large as to be able to cause very 
high velocities of approach by reason of their gravitating influence ; 
or when small masses did happen to collide with a great velocity, 
there would be little or no chance that they would remain together 
after collision, and the heat evolved would soon be dissipated by 
radiation. 
Now supposing the whole mass forming the earth and moon 
