MEASUREMENTS 213 



dictions are absolute, as well as certain and exact, such as 

 the movements of stars and comets, eclipses, and facts like 

 those of astronomy, which are beyond the reach of experi 

 ment. In the second may be placed the weather and other 

 events which are both objective and beyond the reach of 

 experiment, but of which, as our knowledge of the factors 

 is not exact, we can make no certain predictions. A third 

 class is constituted by events in regard to which the pre 

 dictions, though certain and exact, are hypothetical ; that 

 is to say, depend on some condition which is not certain. 

 This class, again, may be subdivided according as the condition 

 is objective or subjective. We may say that if at any time 

 the atmosphere has attained a certain heat, the thermometer 

 will mark so many degrees ; or we may say that if a man 

 puts a match to gunpowder it will explode. In the first, 

 the condition belongs to the unexplored branch of objective 

 science ; in the second, it is a subjective element. If our 

 knowledge were sufficiently advanced, we should be able 

 to predict for an indefinitely remote future the exact moment 

 when the thermometer would mark the given number of 

 degrees ; but no advance in psychology, on its present lines, 

 would enable us to predict the explosion. Many of the 

 predictions of chemistry and other experimental sciences are 

 hypothetical, in the sense that they are never realized 

 except by the intervention of some unaccountable element 

 in the cause ; a sense which, it need scarcely be pointed 

 out, is quite distinct from that in which the word is 

 applied to laws, like those of astronomy, which will always be 

 realized, unless some element, hitherto unaccounted, should 

 supervene. 



Finally, there remains the large class of events of the most 

 urgent interest to ourselves, in which the factors are either 

 wholly subjective or alternately objective and subjective. 

 To these belong religion, ethics, art, history, law, and politics, 

 and, in short, the whole philosophy of human nature. 



The history of science has been the record of the gradual 

 reduction of objective events to series under the law of 

 uniform sequence, and the consequent enlargement of our 



