INTRODUCTION. XI 



The original violent rapidity of the earth's motion might 

 cause a prodigious evaporation of the primeval waters, as 

 in the tail of a comet : and in the general chaos of this 

 solar system some esteem it not impossible that a satellite 

 may have struck a planet, and have merged in it, or have 

 been diffused over it; while the shock may have produced 

 the refoulements of Saussure, which he seems to ascribe to an 

 external cause *$ in which he is followed by Dolomieu, who 

 compares the strata of the globe to the shell of an egg, shat- 

 tered by a squeeze of the hand. Some recent writers have 

 also, on other grounds, adopted the same opinion. 



As therefore, in the ideas of Newton and La Place, strength- 

 ened by many discoveries of pneumatic chemistry, the solar 

 fire must have been a prime agent in the creation, as it is 

 still the chief agent of preservation, generation, and life, it 

 may well be conceived, as nature always proportions the 

 power to the effect, that the heat was at first violent, and 

 gradually diminished to the present temperature. Hence the 

 impressions of plants, which are now tropical, are found in 

 climates at present temperate or frigid. The doctrine of 

 central heat seems now to be universally abandoned, though 

 if the nucleus of the earth consist of iron, according to the 

 writers on magnetism, or of various metals which pass into 

 earths, according to Dr. Davy, it is difficult to conceive that 

 there should not be a certain heat peculiarly modified, as 

 another modification exists in animal lifef. If we judge, 



* De Luc, though a Genevan, acknowledges that he does not understand 

 Saussure's refoulement. Bertrand, another Genevan (Ren. Period. Paris an s), 

 interprets it subversion. Saussure himself distinguishes it from affaissement, and 

 in one passage calls it un refbulement en sens contraire. 



f The nature and varieties of heat and light are far from being ascertained. 

 Saussure, 224", regards them as different substances, and observes that the 

 point of the flame actuated by the blow-pipe, though not of a paler blue than 

 the rest, yet, deprived of light, will convert gold into vapours, and yield the 

 greatest heat excitable by art. But the appearance of light must depend on 

 the degree of darkness, which no means seem to have been invented to 

 increase. 



