8 The Realm of Nature CHAP. 



classes are never so definite as to isolate one from another, 

 the unity of Nature being as marked as its diversity. 



14. Natural Law is the order in which things have 

 been observed to happen. The fact that there is order 

 and not chance in the way things happen is one of the 

 chief discoveries of science. It is the discovery on which 

 all science depends, because knowledge could never be 

 definite and accurate if it were not based on orderly 

 phenomena. It is impossible that there can be any ex- 

 ception to a law of Nature, or any contradiction of it. 

 Much has been written as to the impossibility of miracles 

 because they would be breaches of the laws of Nature. If 

 there is evidence, however, that a miracle did happen, the 

 law of Nature it- appears to contravene must be restated 

 so as to take account of the new phenomenon. It is be- 

 cause the law expands to admit apparent exceptions that 

 we say there can be no exceptions. We have, strictly 

 speaking, no right to assume that things will continue 

 to happen in the order in which they have happened 

 hitherto. Nothing in; time past has been more regular 

 and uniform in its recurrence than the appearance of the 

 Sun rising and setting. This regular order is a natural 

 law, yet we cannot say certainly that the Sun will rise 

 to-morrow ; merely that its rising is very highly probable. 

 The law of gravitation, the laws of heat, light, sound, and 

 of all other observed facts, are similarly the summary of 

 observations in the past ; and although each new verification 

 increases the probability that the laws will continue to hold 

 good, that probability never becomes certainty. 



15. Probability. The probability of 7,000,000 to i 

 is so great that all but very cautious people think of it as 

 certainty. It represented the chance of a passenger arriv- 

 ing alive at the end of a railway journey in the United 

 Kingdom in the year 1890. The probability that the Sun 

 will rise to-morrow is far greater than this, because no 

 failure has ever been recorded in the past. The laws of 

 Nature, although only expressions of very high probability 

 as regards the future, may be assumed as quite certain for 

 all the practical purposes of life. 



