590 On the Evidence that the Earth's Interior ıs Solid. [June, 
Thomson's views were republished and reaffirmed in 18722 but 
in 1876 he says, regarding his previous argument from precession 
and nutation, as the result of a conversation between himself and 
Professor Newcomb : “ Trying to recollect what I had written on 
it fourteen years ago * * * my conscience smote me, and! 
could only stammer out that I had convinced myself that so-and- 
so and so-and-so, at which I had arrived by a non-mathematical 
short cut, were true. He hinted 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 fora 
moment admit, any more than when it was first put forward by 
Delaunay.? But doubt entered my mind regarding the so-and-so 
and so-and-so, and I had not completed the night journey to 
Philadelphia, which hurried me away from our unfinished discus- 
sion, before I had convinced myself that they were grievously 
wrong.” i 
Thomson, however, strongly affirmed the correctness of his 
views regarding the rigidity of the earth as determined by T 
phenomena of the tides. It is permitted, since he still retains 
view that the crust when formed would sink, from its "n 
the center, to think that if he would affirm the pe T 
nutation theory, for fourteen years, sọ often as he had, wi 
giving it sufficient thought, that possibly with the very mp s 
tidal data at his command, he has not looked at this question 
all its bearings. 
Professor Teele indeed in 1872 pointed out that Ta 
had assumed a spheroidal homogeneous elastic shell fi ia 
incompressible fluid, and that all the latter could gine 
proved was, “ that the earth does not consist of an ae si 
envelope enclosing a mass of the ideal substance ¢@ 
compressible liquid.” Hennessy also justly calls i 
the fact that Thomson’s method of proving the rig! glass 
earth by assuming, first, that it is a homogeneous © g, as if om 
and again of steel, is an argument of the same kin siway trains 
should attempt to prove that rapid locomotion 1^ ra 
was impossible, on account of the shocks the passe? 
+ = 260, ee og 
9 ARPES big os Takas, a Hennessy advanced this gen im i) 
enteen years before Delaunay. See Mature, 1871, Ul, 420; Geol. 
VIII, 216-218. 
? Report Brit. Assoc., 1876, xvi (Sect.), I-12. 
