846 EPOCHS IN THE HISTORY OF THE CONTEMPLATION OP 



inflammable gases, exclusively to the admixture of certain 

 vapours. Black and Cavendish first shewed in 1766 that 

 carbonic acid (fixed air) and hydrogen (combustible air) are 

 specifically distinct aeriform fluids. So long had the ancient 

 belief in the elementary simplicity of the atmosphere impeded 

 the progress of knowledge. The final investigation of the 

 chemical composition of the atmosphere, by a most accurate 

 determination of the quantitative relations of its constituent 

 parts by Boussingault and Dumas, is one of the brilliant 

 points of modern meteorology. 



The extension of physical and chemical knowledge, which 

 has been here described in a fragmentary manner, could not 

 remain without influence on the early progress of Geology. 

 A great part of the geological questions with the solution of 

 which our age is occupied, were stirred by a man of the 

 most comprehensive knowledge, the great Danish anatomist 

 Nicolaus Steno (Stenson) in the service of the Grand Duke 

 of Tuscany, by an English physician Martin Lister, and by 

 " Newton's worthy rival/' ( 532 ) Robert Hooke. Steno's 

 merits in respect to the superposition of rocks have been de- 

 veloped by me more fully in another work. ( 533 ) Previously 

 to this period, and towards the end of the fifteenth century, 

 Leonardo da Yinci, probably in laying out the canals in 

 Lombardy which cut through alluvium and tertiary strata, 

 IVacastoro in 1517, on the occasion of seeing rocky strata 

 containing fossil fish accidentally uncovered at Monte Bolca 

 near Yerona, and Bernard Palissy in his investigations 

 respecting fountains, had recognised the traces of a former 

 oceanic world of animal life. Leonardo, as if with the pre- 

 sentiment of a more philosophical division of animal forms, 

 terms the shells " animali che hanno 1'ossa di fuori." Steno, 



