CHAPTER XVI. 



THE METHOD OF MEANS. 



ALL results of the measurement of continuous quantity 

 can only be approximately true. Were this assertion 

 doubted, it could readily be proved by direct experience. 

 For if any person, using an instrument of the greatest 

 precision, makes and registers successive observations in 

 an unbiassed manner, it will almost invariably be found 

 that the results differ from each other. When we operate 

 with sufficient care we cannot perform so simple an 

 experiment as weighing an object in a good balance 

 without getting discrepant numbers. Only the rough 

 and careless experimenter will think that his observations 

 agree, but in reality he will be found to overlook the 

 differences. The most elaborate researches, such as those 

 undertaken in connexion with standard weights and 

 measures, always render it apparent that complete coinci- 

 dence is out of the question, and that the more accurate 

 our modes of observation are rendered, the more numerous 

 are the sources of minute error which become apparent. 

 We may look upon the existence of error in all measure- 

 ments as the normal state of things. It is absolutely 

 impossible to eliminate separately the multitude of small 

 disturbing influences, except by balancing them off against 

 each other. And even in drawing a mean it is to be 

 expected that we shall come near the truth rather than 

 exactly to it. In the measurement of continuous quantity, 



