COSMIC PHILOSOPHY 



suspecting that the heat disengaged by the com- 

 pression of the undulating strata of the air gave 

 additional elasticity, and so produced the differ- 

 ence, made the needful calculations and found 

 he was right. Thus acoustics was arrested until 

 thermology overtook and aided it. When Boyle 

 and Mariotte had discovered the relation be- 

 tween the density of gases and the pressures 

 they are subject to, and when it thus became 

 possible to calculate the rate of decreasing den- 

 sity in the upper parts of the atmosphere, it 

 also became possible to make approximate 

 tables of the atmospheric refraction of light. 

 Thus optics, and with it astronomy, advanced 

 with barology. . . . When Fourier had deter- 

 mined the laws of conduction of heat, and when 

 the earth's temperature had been found to in- 

 crease below the surface one degree in every 

 forty yards, there were data for inferring the 

 past condition of our globe ; the vast period it 

 has taken it to cool down to its present state ; 

 and the immense age of the solar system — a 

 purely astronomical consideration. Chemistry 

 having advanced sufficiently to supply the need- 

 ful materials, and a physiological experiment 

 having furnished the requisite hint, there came 

 the discovery of galvanic electricity. Galvan- 

 ism reacting on chemistry disclosed the metallic 

 bases of the alkalies, and inaugurated the elec- 

 tro-chemical theory ; in the hands of Oersted 



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