52 THE PATH OF SCIENCE 



into coincidence with a mark on a scale, or weighs by ob- 

 serving tlie weight which will enable the pointer of the bal- 

 ance to swing uniformly over the center of the scale. The 

 impersonal data, therefore, that form the basis of scientific 

 knowledge come from judgments of coincidence, and it is 

 only when such determinations of coincidence can be made 

 that general agreement between different observers is found. 

 When men are asked to judge the values of truth or beauty, 

 goodness or merit, there is no approximation to universal 

 agreement; but different observers will agree when they are 

 making coincidence observations. 



It is true that the precision of coincidence observations is 

 limited. A scientist is sometimes asked how he can tell that 

 certain points really coincide. The answer is that the word 

 really has no meaning. Within certain limits, fixed by the 

 sensitivity of the instrument and by the skill of the indi- 

 vidual in judging coincidence, different observers will agree. 

 As Newton wrote in a letter in 1675, dispute about what can 

 be observed in an experiment "is to be decided not by dis- 

 course but by new trial of the experiment." * 



In the observation of facts, the scientist and, indeed, all 

 human beings select some of the facts for attention and do 

 not treat all of them in the same way. Scientific facts repre- 

 sent, indeed, only a very small portion, selected from all the 

 facts that could be observed. The selection depends upon 

 the previous knowledge and upon the interest of the observer. 

 Suppose, of two men entering a room, one was extremely 

 thirsty, and the other was a painter interested in modern art. 

 The first on entering the room ^vould see the jug of water on 

 the table, and, whether or not his manners would restrain 

 him from making a dash at it, the jug ^vould certainly be 

 the center of his interest until his thirst was satisfied. The 

 artist, not being thirsty, would probably not be conscious of 

 the existence of the jug. His interest might be attracted by 

 a picture on the wall. An extreme case of this difference in 



* George, op. cit., p. 100. 



