416 0. Fisher — Rival Theories of Cosmogony. 



value of p (p + s) using s for the surface density. Thus for 

 instance at the depttrof 400 miles, where by Laplace's law the 

 density is 3*88, the compressibility would have to be 3*6069 X 

 10-° -r- 3-88 X (3-88 + 2:75), which makes it 1*4021 X 10" 6 . 

 This may be looked upon as a small compressibility, seeing 

 that the compressibility of water similarly measured is 4*78 X 

 10" 5 or nearly forty times as great. The condensation at this 

 depth would' be (3*88 - 2*75) -*- 3*88 or about 0-29 and conse- 

 quently the linear dimension would be reduced by about one 

 tenth. 



At the center the compressibility similarly measured would 

 be very small, viz., 2*5 X 10" 7 while the condensation would 

 be large, viz., 0*744. 



It appears, therefore, that if matter of the density of rock at 

 the earth's surface can be reduced to the density matter has in 

 the deep interior, it must at one and the same time be capable 

 of being compressed into a much smaller volume than it origi- 

 nally occupied, and also it must be in a condition to require 

 enormous pressure to effect that condensation. Now it does 

 not seem* probable that any solid substance would possess these 

 properties, nor yet a liquid, but a hot gas would. Hence we 

 seem driven to the alternative to enquire whether the deep 

 interior consists of surface rock in the state of a heated gas, or 

 whether it consists of matter such as iron or other metals 

 intrinsically of the required density and either in a solid or 

 a liquid state ; because if the matter be gaseous, there would 

 be no segregation of elements in it. 



The above alternative when applied to the meteoric theory 

 leads us to enquire in the first place whether rocky matter 

 could by any amount of heat be reduced to the state of gas. 

 The competing nebular hypothesis assumes that it can. Sec- 

 ondly, if that be the case, could the gas be compressed until it 

 became more dense than the matter was in its solid state ? It 

 would be difficult to prove that it could not. Thirdly, would 

 the necessary temperature be acquired under these circum- 

 stances ? On this point I have made some calculations, and it 

 appears that the temperatures produced by the condensation 

 would be so inconceivably high that no substance capable of 

 vaporisation could withstand them. 



These calculations cannot of course pretend to any degree 

 of accuracy, because they assume that the specific heat through- 

 out the process of condensation continues as at first, although 

 no increase of specific heat could alter the order of their mag- 

 nitude ; neither do they take account of the latent heat 

 absorbed in passing from the solid to the fluid states. Never- 

 theless the results will be sufficient for the enquiry at hand. 

 But before passing on to the question of temperatures, and 



