which may injluence Geological Phenomena. 299 



mer to the winter solstice^ and thus to produce a transition from the one to 

 the other species of climate, in a period sufficiently great to give room for a 

 material change in the botanical character of a couniry. 



The supposition above made is an extreme, but it is not demonstrated to be 

 an impossible one; and should even an approach to such a state of things be 

 possible, the same consequences, in a mitigated degree, would follow. But 

 if on executing the calculations it should appear that the limits of the excen- 

 tricity of the earth's orbit are really narrow ; and if, on a full discussion of the 

 very difficult and delicate point of the actual effect of solar radiation, it should 

 appear that the mean as well as extreme temperature of our climates would 

 not be materially affected, — it will be at least satisfactory to knoio that the causes 

 of the phaenomena in question are to be sought elsewhere than in the rela- 

 tions of our planet to the system to which it belongs ; since there does not 

 appear to exist any other conceivable connection between those relations and 

 the facts of geology than those we have enumerated, the obliquity of the 

 ecliptic being, as we know, confined within too narrow limits for its variation 

 to have any sensible influence. 



,J. F. W. Herschel. 



2 Q 1 



