DISCOVERIES IN THE CELESTIAL SPACES. 731 



nature, or notice the vivid burning of the flame. Hales 

 had no idea of the importance of the substance he had pre- 

 pared. The vivid evolution of light in bodies burning in oxy- 

 gen, and its properties, were, as many persons maintain, dis- 

 covered independently by Priestley in 1772-1774, by Scheele 

 in 1774-1775, and by Lavoisier and Trudaine in 1775.* 



The dawn of pneumatic chemistry has been touched upon 

 in these pages, with respect to its historical relations, because, 

 like the feeble beginning of electrical science, it prepared the 

 way for those grand views regarding the constitution of the 

 atmosphere and its meteorological changes, which were mani- 

 fested in the following century. The idea of specifically 

 distinct gases was never perfectly clear to those who, in the 

 leventeeth century, produced these gases. The difference 

 between atmospheric air and the irrespirable light-extinguish- 

 ing or inflammable gases, was now again exclusively ascribed 

 to the admixture of certain vapours. Black and Cavendish 

 first showed, in 1766, that carbonic acid (fixed air) and 

 hydrogen (combustible air), are specifically different aeri- 

 form fluids. So long did the ancient belief of the elementary 

 simplicity of the atmosphere check all progress of know- 

 ledge. The final knowledge of the chemical composition of 

 the atmosphere, acquired by means of the delicate discrimi- 

 nation of its quantitative relations, by the beautiful researches 

 of Boussingault and Dumas, is one of the brilliant points of 

 modern meteorology. 



The extension of physical and chemical knowledge, which 

 we have here brie-fly sketched, could not fail to exercise an 

 influence on the earliest development of geognosy. A great 

 number of the geognostic questions, with the solution of 

 which our own age has been occupied, were put forth by a 

 man of the most comprehensive acquirements, the great 

 Danish anatomist, Nicolaus Steno (Stenson), in the service 

 of the Grand Duke of Tuscany, Ferdinand II. ; by another 

 physician, Martin Lister, an Englishman, and by Robert 

 Hooke, the " worthy rival" of Newton.f Of Steno's ser- 



* Priestley's last complaint of thpt which " Lavoisior is considered to 

 have appropriated to himself," is put forth in his little memoir entitled, 

 " T\e Doctrine of Phlogiston established" 1800, p. 43. 



t Sir John Herschel, Discourse on the Study of Natural Philoso* 

 phy p. 116. 



