CHAPTEE XVT. 



THE METHOD OF MEANS. 



,All results of the measurement of continuous quantity 

 can be only approximately true. Were this assertion 

 doubted, it could readily be proved by direct experience. 

 If any person, using an instrument of the greatest pre- 

 cision, makes and registers successive observations in 

 an unbiassed manner, it will almost invariably be found 

 that the results differ from each other. AVhen 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 

 difTerences. The most elaborate researches, such as those 

 undertaken in connection 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 u])on 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. 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, absolute 

 coincidence, if it seems to occur, must be only apparent, 

 and is no indication of precision. It is one of the most 

 embarrassing things we can meet when experimental 



