342 Address of Sir Wm. Thomson at the Glasgow Meeting. 
voleanic regions occupied by liquid lava: but whatever portion 
of the whole mass is liquid, whether the waters of the ocean or 
melted matter in the interior, these portions are small in com- 
parison with the whole, and we must utterly reject any geologi- 
ypothesis which, whether for explaining underground heat 
or ancient upheavals and subsidences of the solid crust, or 
earthquakes, or existing volcanoes, assumes the solid earth to 
be a shell of 30, or 100, or 500, or 1,000 kilometers thickness, 
resting on an interior liquid mass. 
This conclusion was first arrived at by Hopkins, who may 
therefore properly be called the discoverer of the earth’s solidity. 
He was led to it by a consideration of the phenomena of pre- 
cession and nutation, and gave it as shown to be highly prob- 
able, if not absolutely demonstrated. by his confessedly imperfect 
and tentative investigation. But a rigorous application of the 
perfect hydrodynamical equations leads still more decidedly to 
the same conclusion. 
I am able to say this to you now in consequence of the con- 
versation with Professor Newcomb to which I have already 
alluded. Admitting fully my evidence for the rigidity of the 
earth from the tides, he doubted the argument from precession 
and nutation. Trying to recollect what I had written on it 
fourteen years ago in a paper on the Rigidity of the Earth, 
published in the Transactions of the Royal Society, my con 
science smote me, and I could only stammer out that ad 
convinced myself that so and so, and so and so, at which I had 
arrived by a non-mathematical short cut, were true. He hint 
that viscosity might suffice to render precession and nutation 
the same as if the earth were rigid, and so vitiate the argument 
for rigidity. This I could not for a moment admit any more 
than when it was first put forward by Delaunay. But doubt 
on prvocssion and nutation of an elastic yielding of the 
ce 
surface, i 
When those passages were written I knew little or nothing of 
vortex motion; and until my attention was recalled to t pce 
Professor Newcomb, I had never once thought of ins Siaity 
in the light thrown upon it by the theory of the quasr7! 
