300 THE PRINCIPLES OF SCIENCE. 



them. Inferences pushed far beyond their data soon lose 

 any considerable probability. De Morgan has said d , ' No 

 finite experience whatsoever can justify us in saying that 

 the future shall coincide with the past in all time to come, 

 or that there is any probability for such a conclusion.' On 

 the other hand, we gain the assurance that experience 

 sufficiently extended and prolonged will give us the 

 knowledge of future events with an unlimited degree of 

 probability, provided indeed that those events are not 

 subject to arbitrary interference. 



It must be clearly understood that these probabilities are 

 only such as arise from the mere happening of the events, 

 irrespective of any knowledge derived from other sources 

 concerning those events or the general laws of nature. 

 All our knowledge of nature is indeed founded in like 

 manner upon observation, and is therefore only probable. 

 The law of gravitation itself is only probably true. But 

 when a number of different facts, observed under the most 

 diverse circumstances, are found to be harmonized under a 

 supposed law of nature, the probability of the law approxi- 

 mates closely to certainty. Each science rests upon so 

 many observed facts, and derives so much support from 

 analogies or direct connections with other sciences, that 

 there are comparatively few cases where our judgment of 

 the probability of an event depends entirely upon a few 

 antecedent events, disconnected from the general body of 

 physical science. 



Events may often again exhibit a regularity of suc- 

 cession or preponderance of character, which the simple 

 formula will not take into account. For instance, the 

 majority of the elements recently discovered are metals, 

 so that the probability of the next discovery being that of 

 a metal, is doubtless greater than we calculated (p. 298). 

 At the more distant parts of the planetary system, there 



d 'Treatise on Probability,' Cabinet Cyclopaedia, p. 128. 



