534 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
The matter we have to deal with is all of it plastic and viscous. The 
pressure of a quick blow makes a glass rod give out a musical ring, and a 
harder, quicker blow may break it to fragments; but the same pressure 
long continued will produce neither sound nor fragments, but will mold 
the glass into any shape we please. 
It is evident that every form of matter as we know it on this earth be¬ 
comes viscous fluid under the influence of either temperature or pressure, 
and the pressures within the earth’s surface at a comparatively short 
depth are sufficient to make all known rocks behave like viscous fluids, 
without any special increase of temperature. 
It is therefore evident that our earth, under the influence of the cen¬ 
trifugal force due to its diurnal rotation, would assume its present sphe¬ 
roidal shape without the necessity of being any more truly a fluid than 
it is at the present moment. 
We thus remove what to me has always seemed a great difficulty, both 
from geological and from thermo-dynamic considerations, namely, the 
assumption that the earth was at one time a molten globe. There is 
evidently no longer any need of making such assumption, and in fact 
still other considerations that I need not now enumerate have of late 
made me feel the propriety of wholly rejecting this idea as a necessity in 
any cosmogony. 
It is now evident that any irregular meteoric mass that is a mixture of 
materials like those of our earth, and as large as it, must under the in¬ 
fluence of its own gravitation, assume a spherical form and have a greater 
density at its center than its circumference, owing not only to the presence 
there of denser forms of matter, but especially to the general compression 
due to pressure. On the other hand, irregularities would continue to exist 
on the surface, but to such an extent only as is allowed by the fact that 
the pressures there are less, and consequently the relative rigidity greater. 
Again, such a viscous, but rough-surfaced, globe entering the solar sys¬ 
tem and acquiring a rotation would, under the long-continued influence 
of its own axial rotation, assume a spheroidal shape. 
In doing this the change of shape from sphere to spheroid would, through 
internal friction and stress, produce considerable internal heat, which I 
would designate as its initial heat. The diurnal rotation of such a globe 
in the presence of the sun and moon also gives rise to the bodily tides 
recently investigated by Mr. G. IT. Darwin and Sir William Thomson. 
Sea water is so limpid that it can have an appreciable diurnal tide, but 
the diurnal bodily tides are too rapid to produce large deformations in 
the very viscous, dense body of our earth; however, they can produce 
temporary strains, whose effect I will explain at some future date. On the 
other hand, the fortnightly lunar tide, however, can produce a continual 
deformation of the viscous and plastic mass of our earth, and give rise to 
an internal friction such as occurs in every fluid when the molecules 
move past each other. This friction we recognize in another form as in¬ 
ternal heat, so that in fact lunar gravitation (and possibly solar gravita- 
