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March 15, 1849. 



The MARQUIS OF NORTHAMPTON, V.P., in the Chair. 



A paper was read, entitled " Researches in Physical Geology." 

 Part 11. By Henry Hennessv, Esq. Communicated by Major 

 Beamish, F.R.S. 



In this communication the author states that, having in Part I. 

 (read to the Society in December 1846) endeavoured, by general- 

 izing the hypothesis on which is usually founded the theory of the 

 earth's figure, not only to improve that theory, but also to establish 

 a secure basis for researches into the changes which may have taken 

 place, within and at the surface of the earth, during the epochs of 

 its geological history, his object here is to discover relations between 

 the interior structure of the earth and phenomena observed at its 

 surface, and also the effects of the reaction of the fluid nucleus, de- 

 scribed in Part I., upon the solid crust. This memoir is divided 

 into sections, each containing a distinct investigation ; and the state- 

 ment of the geological results is given at the end. 



I. The Pressures of the Shell and Nucleus at their surface of contact. 



In the investigation of these pressures the earth is supposed to 

 consist of a nucleus of fluid matter inclosed in a solid shell, the inner 

 and outer surfaces of which are spheroidal, but nearly spherical ; 

 and both shell and nucleus are supposed to consist of strata varying 

 in density according to some unknown inverse law of the radii. The 

 pressure at the inner surface of the shell is conceived to be due to a 

 constant pressure, which is the same for every point, and a variable 

 pressure, arising from the difference in form of the surface of the 

 nucleus and inner surface of the shell. On these suppositions, simple 

 expressions for the pressure on any stratum of the nucleus and on 

 the shell's inner surface are deduced. 



II. The Variation of Gravity at the earth's surface. 



The author does not assume in this investigation that the laws of 

 arrangement of the particles composing the shell and the nucleus 

 are necessarily the same ; so that the expression which he obtains 

 for gravity at any point on the earth's surface, besides being a func- 

 tion of the latitude of that point, and of the radii and ellipticities of 

 the shell's inner and outer surfaces, contains functions depending on 

 the constitution of the shell and nucleus. He states that this ex- 

 pression for gravity is not merely speculative, but that it will be 

 found to assist in explaining certain apparent anomalies detected by 

 observation in the variation of gravity at the earth's surface, as well 

 as in pointing out the limits assigned by observation to the thickness 

 of the crust. 



III. The Laws of Density of the Shell and Nucleus. 



According to the author's views in a subsequent section, it ap- 

 pears that the solidification of the earth could not proceed simulta- 



