206 COSMIC PHILOSOPHY. [pt. i. 



.... Let us look at a few cases. The theoretic law of the 

 velocity of sound, enunciated by Newton on purely mecha- 

 nical considerations, was found wrong by one-sixth. The 

 error remained unaccounted for until the time of Laplace, 

 who, suspecting that the heat disengaged by the compression 

 of the undulating strata of the air, gave additional elasticity 

 and so produced the difference, 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 between the density of gases and 

 the pressures they are subject to ; and when it thus became 

 possible to calculate the rate of decreasing density 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 determined the laws of 

 conduction of heat, and when the earth's temperature had 

 been found to increase 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 needful materials, and a 

 physiological experiment having furnished the requisite hint, 

 there came the discovery of galvanic electricity. Galvanism 

 reacting on chemistry disclosed the metallic bases of the 

 alkalies, and inaugurated the electro-chemical theory ; in the 

 hands of Oersted and Ampere it led to the laws of magnetic 

 action; and by its aid Faraday detected significant facts 

 relative to the constitution of light. Brewster's discoveries 

 respecting double refraction and dipolarization proved the 

 essential truth of the classification of crystalline forms 

 according to the number of axes, by showing that the 

 molecular constitution depends upon the axes. In these, and 

 in numerous other cases, the mutual influence of the sciences 



