THE UNIFORMITY OF NATURE. 255 



say that to the mathematician the language involves a necessary- 

 catastrophe, and that if the sun did stand still, even for a moment, no 

 one would be left to tell the tale. 



It is true that all men are not mathematicians, and that it is im- 

 possible for a mind which has not studied physical science mathemati- 

 cally fully to estimate the impression of contradiction and impossibili- 

 ty produced upon the mind which has so studied by an allegation of 

 any irregularity in the clock of Nature. Be it observed that the be- 

 lief in the uniformity of such a phenomenon as the rising of the sun, 

 or of the effect of the moon on the tides, or of such observed facts 

 as precession and nutation, and many others, is to the mathematical 

 physicist something different in kind from that which arises from 

 mere experience. If you say that the sun has risen millions of times 

 already, and therefore will probably, or almost certainly, rise to-mor- 

 row, you offer a good presumptive argument ; but it is not the argu- 

 ment which chiefly weighs with the man who knows what the rising 

 of the sun means, and what would be the mechanical result of his fail- 

 ing to do so. My belief, however, is, that the feeling of certainty as 

 to natural phenomena, which such men as Laplace felt for the first 

 time in human history, has percolated (so to speak) through the strata 

 of human intelligence until it has become the common property of 

 almost all. The whole aspect of jSTature has been changed ; and many 

 a man feels a persuasion of the existence of something which may be 

 described as uniformity, and in virtue of which he questions or doubts 

 or denies many things which would have been accepted as possible or 

 probable in the seventeenth century, without knowing or being able 

 to explain upon what his convictions rest. 



Hence, according to my view, the uniformity of Nature, instead of 

 being capable of being defended as a postulate, is, so far as it is true, 

 the result of very hard scientific fighting. In the region of celestial 

 mechanics it may be said to have gained absolute sway, because the 

 motions of the heavens resolve themselves into the ordinary laws of 

 mechanics, supplemented by the law of universal gravitation ; and 

 from this region there is a very intelligible tendency to extend the 

 assertion of the principle to other departments of scientific investi- 

 gation. Such extension, however, must be made with caution ; even 

 in the solar system itself, the moment we go beyond mechanics, all 

 uniformity appears to vanish. With regard to size, arrangement, 

 density, in fact every element of planetary existence, variety, which 

 defies all kind of classification, not uniformity, is the undoubted order 

 of Nature. 



There is a striking paragraph on this subject from the pen of no 

 less a man than Alexander von Humboldt, which it may be well to 

 quote in this connection. After speaking of the absence of all known 

 law connecting the various planetary elements, their magnitudes, 

 densities, etc., he proceeds thus : 



