Physical Structure of the Earth. 



245 



liquide a Fetat solide une alteration sensible par laquelle 

 toutes les couches se sont constituees de maniere a avoir un 

 mime applatissement et plus grand que le precedent." M. 

 Plana has further stated his views in the same volume of the 

 Astronomische Nachrichten for 1852, thus : — " II est permis de 

 penser que ces couches (de la fluide interieuse) en se consoli- 

 dant, ont subi des modifications a la verite fort petites, mais 

 assez grandes pour nous empecher de pouvoir deriver, avec 

 tout l'exactitude que Ton pourrait souhaiter, Fetat de la Terre 

 solide de son etat anterieure de fluidite." 



This paragraph gives a distinct adhesion to the improved 

 form of the hypothesis of the original fluidity of the Earth ; 

 and this concurrence on the part of M. Plana is the more im- 

 portant, as it is possible that he had formed his conclusions 

 independently. He refers to a letter written by him on the 

 subject to Humboldt ; and it is remarkable that, in the fifth 

 and last volume of ' Cosmos,' published not long before the 

 author's death, some adjacent notes allude to Plana's views, 

 and contain references to the investigations of Mr. Hopkins 

 and to my early researches. At this period Humboldt could 

 scarcely have had time to examine the mechanical and physical 

 reasonings, and he merely quoted the papers in the ' Philo- 

 phical Transactions ' as if he had seen them for the first time. 

 I am not aware of any evidence as to whether Plana had 

 known their contents ; and it is possible that his conclusions 

 as to the forms of the strata of the shell and nucleus had been 

 formed independently, though published a short time after my 

 investigations. 



The annexed figure may assist 

 in making clear the results of 

 the preceding paragraphs. The 

 outer ellipse represents the out- 

 line of the exterior surface of the 

 Earth's crust, which is shaded 

 and bounded inwardly by a sur- 

 face slightly more elliptical. The 

 fluid nucleus included within the 

 shell is represented with strata 

 decreasing in ellipticity towards 

 the centre. This arrangement 

 is necessarily followed by a mass ! 



of fluid under such conditions 



as the nucleus, or under the conditions of the entirely fluid 

 Earth. If the matter composing the Earth underwent no 

 change in passing from the fluid to the solid state, instead 

 of the arrangement here represented, the inner surface of the 



