THE LA W OF ERROR. 463 



always possible, and usually likely, that we overlook 

 sources of error which a future generation will detect. 

 Thus the pendulum experiments of Baily and Sabine 

 were directed to ascertain the nature and amount of a 

 correction for air resistance, which had been entirely mis- 

 understood in the experiments upon which was founded 

 the definition of the standard yard, by means of the 

 seconds pendulum in the Act of 5th George IV. c. 74. 

 It has already been mentioned that a considerable error 

 was discovered in the determination of the standard 

 metre as the ten-millionth part of the distance from the 

 pole to the equator (p. 368). 



We shall return in the second volume to the further 

 consideration of the methods by which we may as far as 

 possible secure ourselves against permanent and undetected 

 sources of error. In the meantime, having completed the 

 consideration of the special methods requisite for treating 

 quantitative phenomena, we must return to our principal 

 subject, and endeavour to trace out the course by which 

 the physicist, from observation and experiment, collects 

 the materials of natural knowledge, and then proceeds 

 by hypothesis and inverse calculation to educe from them 

 the laws of nature. 



END OF THE FIRST VOLUME. 



