CHAPTEE XVII. 



THE LAW OF ERROR. 



To bring error itself under law might seem beyond 

 human power. He" who errs surely diverges from law, 

 and it might well be deemed hopeless to suppose that out 

 of error we can draw truth. One of the most remarkable 

 achievements of the human intellect is the establishment 

 of a general theory which not only enables us among dis- 

 crepant results to approximate to the truth, but to assign 

 the degree of probability which fairly attaches to this con- 

 clusion. It would be a gross misapprehension indeed to 

 suppose that this law is necessarily the best guide under 

 all circumstances. Every measuring instrument and every 

 form of experiment may have its own special law of error ; 

 there may in one instrument be a tendency in one direc- 

 tion and in another in the opposite .direction. Every pro- 

 cess has its peculiar liabilities to mistake and disturbance, 

 and we are never relieved from the necessity of vigilantly 

 providing against such special difficulties. The general 

 Law of Error is the best guide only when we have ex- 

 hausted all other means of approximation, and still find 

 discrepancies, which are due to entirely unknown causes. 

 We must treat such residual differences in some way or 

 other, since they will occur in all accurate experiments, 

 and as their peculiar nature and origin is assumed to be 

 unknown, there is no reason why we should treat them 

 differently in different cases. Accordingly the ultimate 

 Law of Error must be a uniform and general one. 



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