434 Archdeacon Pratt on the Fluid Theory of the Earth. 



that supposed distribution would be no medley and without a 

 law ; its law, however, would be so singular as to make the hy- 

 pothesis on which its existence depends utterly untenable. The 

 matter at the various points of the earth, in excess or defect of 

 that required by the 'fluid-law, must be of that precise amount 

 that by its imaginary transference by complete spherical concen- 

 tration or expansion, and by no other process, the fluid-arrange- 

 ment would be exactly attained, no matter left in excess in any 

 point throughout the whole mass, and none in defect. My critic 

 seems to lose sight of the extreme peculiarity of this departure 

 from the fluid-law of distribution, when he says that "it need 

 not be inconsistent with the ascertained variations of gravity if 

 there were distributed irregularly through the earth very dense 

 masses of matter, and likewise cavities filled with very light forms 

 of matter." But his readers will probably not suspect, after read- 

 ing these words, that those " dense masses " must consist of mat- 

 ter following the fluid-law plus masses lying in complete and uni- 

 formly thick and uniformly dense spherical shells, and that those 

 "light forms of matter" also must follow the same precise law, 

 viz. the fluid-law minus complete spherical shells, as before. Any 

 departure from this singular distribution which analysis (hardly 

 nature) has devised, would at once be fatal to the hypothesis. It 

 may perhaps be said that these shells need not be precisely sphe- 

 rical ; that is, they need only be nearly spherical, so as to intro- 

 duce no sensible effect on pendulum experiments. But though 

 this may appear to modify the case, it by no means removes the 

 difficulty which the peculiarity of the arrangement presents. To 

 my own mind these hypothetical departures from the fluid-distri- 

 bution, which are possible according to the integral calculus, 

 cannot be entertained for one moment in the face of the physical 

 curiosities they would introduce. 



Should there be any other varieties of the imaginary body 

 besides spherical shells, the same remarks will apply. 



6. Let me conclude by making some remarks on my reviewer's 

 observation, "We do not see the need of having any theory at 

 all." If this refers to any theory of the earth's origin, I do not 

 see any reason to object to his remark ; because it must be a 

 matter of speculation, so far as science can feel its way. But if 

 he refers to the theory of the earth's having been once in a fluid 

 state, I would say (1) that if the earth's mass is now distributed 

 in a manner which coincides with the arrangement it would have 

 were it a fluid mass, it is so very easy and innocent an induction 

 to pass from the one to the other, without incurring the charge 

 of wild speculation, that it seems allowable ; and (2) that not a 

 single step has been made, that I am aware of, towards determi- 

 ning the figure of the earth (beyond its being merely a more or 



