INTRODUCTION. 8 1 



in which equilibrium was sustained by centrifugal force and 

 gravity. As the glowing mass became denser the centri- 

 fugal force increased, and peripheral rings of vapour similar to 

 those of Saturn separated from the main body. The detached 

 rings continued to move with the same rate and direction of 

 motion as before. Not being of uniform density, they became 

 rent, the different masses formed themselves into rotating 

 spheres, the larger bodies absorbed a part of the smaller, and 

 thus the planets and their satellites took origin. 



The condensation of the vaporous material during the 

 process of aggregation of the particles into spheroids set free 

 a large amount of heat and the newly-formed bodies were 

 raised to a very high temperature; they became radiant 

 masses, radiating light and heat into surrounding space. 

 Owing to the loss of heat by radiation, the surface cooled and 

 shrivelled, and finally a superficial crust formed, at first 

 glowing, afterwards darkening down to its present state. 



According to Laplace, the zodiacal light represents certain 

 volatile unconsolidated parts of the solar atmosphere that still 

 surround the sun ; while the comets are regarded by Laplace 

 as foreign to the solar atmosphere, belonging probably to the 

 infinite space beyond. 



The nebular theory of Kant and Laplace was in far better 

 agreement with the laws of mechanics and the observations of 

 astronomy than any previous cosmogonetic hypothesis. It 

 also helped greatly to elucidate the earliest beginnings of the 

 earth, and was welcomed by geologists. Clearly it brought 

 confirmation to Volcanistic doctrines, and militated against 

 the Neptunian teaching that the primitive crystalline rocks 

 were of aqueous origin. 



Local Geognostic Descriptions and Stratigraphy. A. Ger- 

 many. The revolutionary tendency of the empirical methods 

 taught by Werner in his system of geognosy is displayed in the 

 numerous local monographs that began to appear in all parts 

 of Europe. Both in mineralogy and in stratigraphy, the chief 

 contingent of new work came from the Wernerian school. 



Georg Lasius (1752-1833), who for a long time held the 

 post of Director of the Survey Department in Oldenburg, was 

 no Wernerian, but he contributed a work on the Harz district 

 that ranks among the best and most careful local descriptions 

 of his time. While Lasius was an officer in the Hanoverian 



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