Archdeacon Pratt on the Fluid Theory of the Earth. 433 



before us this body is to possess the property that its external 

 attraction is zero, and its surface is to lie wholly within the 

 earth's surface. For brevity I shall henceforth call such a body 

 " the Imaginary Body/' 



The conclusion, then, to which the above statement of the case 

 leads is this — that the arrangement of the earth's mass must be 

 either 



(1) The fluid-arrangement, or 



(2) The fluid-arrangement + the imaginary body. 



The high physical improbability of this latter I am now to 

 show. 



5. It will be observed that it is impossible altogether to get free 

 from the fluid-arrangement. In any arrangement of the mass 

 which differs from it and suits the problem, still that arrange- 

 ment consists of the fluid-arrangement with some other precise 

 arrangement superadded. I will take the example which my 

 critic produces, and will make use of his diagram (p. 149, Phil. 

 Mag. for February). The distribution of the materials in this 

 particular case is this : everywhere it follows the fluid-law, except 

 along the surface of two spherical shells C and D ; but even 

 there the fluid-law has a controlling influence ; for the distribu- 

 tion along those surfaces is that of the fluid-law in the case of C, 

 minus a precisely equal quantity of matter from every equal ele- 

 mentary portion of the surface and from exactly the same depth 

 (i. e. the thickness of the shell), neither more nor less from any 

 part of the whole spherical surface all round, and in the case of 

 D plus precisely the same amount of matter which is taken from 

 C, and this to be distributed uniformly all over the surface of D 

 and to a uniform depth all round. Such a local and, I will call it, 

 freakish departure from the law of the rest of the mass may be 

 mathematically possible, as it undoubtedly is ; but I regard it as 

 physically inadmissible. For this reason it was that I rejected the 

 thought, as already related, as soon as it occurred to me. If a 

 vera causa could be shown for such a singular distribution, I 

 would at once yield the point, strange as such a distribution 

 would be. It is, however, a mere analytical figment, which in 

 my opinion is of no value in this problem. 



But the incongruous result to which the hypothesis of this 

 single pair of complementary shells leads may no doubt be dis- 

 guised (but only disguised) by imagining the superposition of 

 countless numbers of pairs of complementary shells, of all sizes, 

 intersecting and crossing in endless variety, so as to reduce the 

 mass, in the view of an imaginary eye which could survey all its 

 parts, to a complete medley, and yet the external attraction would 

 be unaffected and the surface-spheroid undisturbed, while the 

 fluid -distribution was to all appearances utterly destroyed. But 



