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XXII. Researches in Terrestrial Physics . — Part II. By Henry Hennessy, 
M.R.I.A. Sfc. Communicated by Major Ludlow Beamish, F.R.S. 
Received February 8, — Read March 15, 1849. 
Preliminary Remarks. 
In the first part of these researches, I have endeavoured, by generalizing 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 v^hich 
may have taken place within and at the surface of the earth during the epochs of its 
geological history. Although I stated that no precise physical evidence could be 
adduced for the examination of the assumption that the molecules of the primitive 
fluid, supposed to have constituted the earth, retained their positions after solidifica- 
tion, it yet appears that such evidence exists, if we may be permitted to draw any 
conclusions relative to the physical properties of substances in the earth’s interior, 
from the observed physical properties of substances at its surface. Professor Bischop 
of Bonn, has shown* that Granite contracts in volume in passing from the fluid to 
the solid crystalline state, from 1 to ‘7481, Trachyte from 1 to ‘8187, and Basalt 
from 1 to *8960. The first of these rocks appears, as far as can be observed, to con- 
stitute the greater part of the earth ; hence the assumption alluded to must be con- 
sidered not only as superfluous, but as erroneous. 
In this Part it is my object 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, described in Article 6, Part I., upon the solid crust. I divide 
this Part into sections, each containing a distinct investigation, the order of arrange- 
ment of these sections being determined according to their fundamental importance. 
The statement of the geological results capable of being deduced from these investi- 
gations is, for greater clearness, reserved for the end. Such of these results as chiefly 
depend on the validity of the reasonings used in Section III. are presented with some 
diffidence, owing to the imperfect experimental knowledge we possess respecting the 
subjects discussed in that section. The diminution of the earth’s mean radius by refri- 
geration is neglected all through, except where the contrary is specially mentioned. 
1. 'FHE PRESSURES OF THE SHELL AND NUCLEUS AT THEIR SURFACE OF CONTACT. 
1. In this investigation the earth is supposed to consist of a nucleus of fluid 
matter inclosed in a solid shell. The inner and outer surfaces of the shell are sup- 
* Leonhard und Bronn’s Neues Jahrbuch, 1841, p. 565. See also a paper by the same writer in the N. 
Jahrbuch for 1843, p. 1. These results seem also to be confirmed by others subsequently found by M. Devillk. 
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