184 SCIENTIST 



the tools for telling whether something is better or worse, 

 or prettier or plainer than something else. 



There are at least two advantages that are derived from 

 the devising of tools to measure the qualities of objects. The 

 first is that it enables us to agree about these qualities much 

 more easily. The second is that we can describe the qualities 

 in terms of numbers and thus enUst the powerful tool of 

 mathematics in describing the relations between objects. It 

 has already been pointed out that the business of ensuring 

 agreement among all conscientious and informed observers 

 is not merely a nice feature of science; it is one of the most 

 important reasons for beheving that science gives us some- 

 thing like a "true" picture of the world. Indeed, many 

 thoughtful scientists who follow the philosophical school of 

 thought known as Operationahsm hold that the only way 

 we can tell that a given experiment leads to valid knowledge 

 and that any general proposition derived from it is true, 

 is that we can describe the necessary operations in such 

 a way that other people can carry them out and get the 

 same results. 



We are all so used to measuring things that we may over- 

 look some of the more interesting features of the process. 

 Notice, for example, that all the comparisons mentioned 

 above as examples of measurements can be made at least 

 fairly well by any natural or untrained man with his un- 

 aided senses. By merely looking at objects we can tell that 

 some are larger than others, some are brighter and have 

 different colors from others, and so on. To early man, all 

 these attributes were thought of as qualities of the objects 

 themselves. Some especially thoughtful man began to won- 

 der, however, whether these qualities really were part of 

 the objects or whether the sensations and perceptions pro- 

 duced in the observers weren't just as, or perhaps even 

 more, dependent on the nature of the observer. One of the 



