THE APPLICATIONS OF SCIENCE 171 



argument, always believed, on the authority of some 

 family tradition of unknown origin, that the walk they 

 took every Sunday afternoon was eight miles long ; and 

 yet a party which was not specially athletic, starting after 

 three, always accomplished it before five. A glance 

 at a map which was hanging in their house would have 

 shown them it was barely six miles. This will doubtless 

 seem a very extreme example concerning a very trivial 

 matter, but parallels can be found readily in matters 

 of considerable importance. During the war it was 

 almost a sufficient reason for the army chiefs to adopt 

 some device that it was known (or more often believed) 

 that the enemy made use of it ; and anyone who comes 

 into contact with unscientific managers of industry will 

 be amazed to find how largely their practice is based on 

 hearsay information, and how little evidence they have 

 that the information was reliable or even given in good 

 faith. 



In matters which lie outside their own sphere, men of 

 science are often as credulous as anyone else ; but in 

 that sphere, if they are really men of science, intimately 

 acquainted with their study by the actual practice of 

 it, they cannot fail to have learnt how dangerous it is 

 to believe any statement, however firmly asserted by 

 high authority, unless they have tested it for themselves. 

 The necessity for the obtaining of information by direct 

 experiment is embedded in their nature, and no informa- 

 tion attained by other means will satisfy them per- 

 manently. The determination to believe what is true, 

 and not what other people assert to be true, is the first 

 and not the least important correction applied by science 

 to popular errors. 



But if there were no other source of error, reliance on 

 hearsay would not be so dangerous, for our informants 

 would not be so likely to be wrong. There would still 

 be the possibility that they intended to mislead us, 



