of the Terrestrial Globe. ^m 



geological phenomena, allows that the succession of ages might 

 bring the eccentricity of the terrestrial orbit to the proportion of 

 that of the planet Pallas, that is to say, to be the ^^^^ of a semi- 

 greater axis. It is exceedingly improbable that in these periodi- 

 cal changes, the eccentricity of our orbit should ever experience 

 such enormous variations ; and, even then, these twenty-five 

 hundredth parts (//c), would not augment the mean annual 

 solar radiation, except by about one hundredth part (j J^). To 

 repeat, an eccentricity of //jy would not alter in any appreciable 

 manner the mean thermometrical state of the globe. It would 

 only follow, that at an interval of six months, the greatest dis- 

 tances, and the least from the earth to the sun, which now dif- 

 fer scarcely a thirtieth (55), would then be in the ratio of 5 to 

 3. At comparative distances of 3 and 5, the illuminating and 

 heating intensities of the sun, would be, between them, nearly as 

 3 to 1 . Let us now, then, grant the intensity of three to the 

 summer solstice, — ^in other words, let us place three suns over 

 our heads in the months of July and August, and we shall form 

 a tolerably correct idea of the excessive heat which we should 

 experience during certain days^ if the eccentricity of our orbit 

 were twenty-five hundredths dVo)- I cannot, however, too of- 

 ten repeat, that such an eccentricity can probably never occur ; 

 and, at all events, we cannot find it, in going back upon the past, 

 even as far as fifteen or twenty thousands of years, of our pre- 

 sent epoch. 



VII. Of Terrestrial ClimateS) as they may he hnovmfrom Observa 

 tions made in different Ages, 



Thus, then, have we disencumbered, so far at least as it re- 

 gards the phenomena which exhibit themselves at the surface, 

 the problem of terrestrial temperatures, of many elements which 

 have greatly complicated it. We have found that the central 

 heat could not occasion any sensible variation of climate, since 

 its wh^le effect at the surface, does not now exceed one-thirtieth 

 (M o^ ^ degree. The temperature of space, whatever doubts 

 may yet remain as to the value which Fourier has assigned 

 to it, must remain very nearly constant, if its cause, as every 

 thing leads us to believe, is the stellary radiation. The changes 

 Off the form, and of the position, of the terrestrial orbit, are ma- 



