158 Successful prediction a test of truth. 



The highest test of truth is verified prediction ; 

 if we calculate beforehand that an eclipse of the Sun 

 will occur at a certain hour and minute, and that 

 eclipse occurs accurately at the predicted moment, we 

 may rest assured that our knowledge upon that point 

 is true and complete. If we say that a piece of clean 

 iron, immersed in a solution of blue vitriol, will become 

 covered with a layer of metallic copper, and we find 

 upon trial that this result invariably occurs when we 

 fulfil those conditions, we may be certain that our 

 knowledge of this phenomenon and its conditions is 

 also of a definite and certain character. Similarly, 

 when we become able to predict with certainty the 

 conditions of the Sun's surface, we shall probably also 

 be able to predict severe winters, famines, &c., and 

 therefore be prepared to suggest precautions to be 

 taken against them. Even now the new truth neces- 

 sary for this purpose is beginning to be evolved by 

 means of scientific research.* 



Amongst the great axioms and principles of 

 science, possessing great certainty, and which enable 

 us to predict, are, 1st. the general truth known as the 

 Principle of Causation, that every effect has a cause; 

 that the same cause, acting under the same conitions, 

 always produces the same effect ; and that causation 

 acts through all time arid all space : 2nd. the 

 great truth, that every phenomenon requiries time ; 

 and every substance occupies space : $rd. the 

 Principles of Conservation and Persistency of Matter 



* See "Barometer Cycles," by Balfour Stewart, F.R.S. Nature, Jan. 13. 

 1881, p, 237. 



