THE SCIENTIFIC MOOD. 9 



differ, though the difference may be measured by 

 less than the thousandth of a milligramme or of a 

 millimetre, or by any other like standard of minute- 

 ness. And the man who, carrying the ways of the 

 world into the domain of science, thinks that he may 

 treat Nature's differences in any other way than she 

 treats them herself, will find that she resents his 

 conduct ; if he in carelessness or in disdain overlooks 

 the minute difference which she holds out to him as 

 a signal to guide him in his search, the projecting 

 tip, as it were, of some buried treasure, he is bound 

 to go astray, and, the more strenuously he struggles 

 on, the farther will he find himself from his true 

 goal."* 



Many people most excellent in virtues seem 

 constitutionally incapable of accurately reporting an 

 occurrence ; many more seem quite unable to see the 

 difference between an observation and an inference. 



The scientific worker is himself well aware 

 that, in measurements and observations, only an 

 approximate accuracy can be attained, and that 

 the degree of approximation varies with the indi- 

 vidual. But this relativity of accuracy is far from 

 being generally recognised, and scientific state- 

 ments often get credit for a precision which they 

 do not claim. The personal equation has been for 

 a long time frankly recognised and allowed for in 

 astronomy; it is also sometimes estimated in chem- 

 istry and physics,f but we hear too little of it in 

 the less exact sciences such as biology and psy- 

 chology. 



Even apart from intellectual training, may it not 

 be claimed that the discipline of the chemical balance, 



* Sir Michael Foster, loc. cit. p. 16. 

 f See Ostwald's Text-book of General Chemistry. 



