164 EMPIRICAL TOOLS AND EMPIRICISM 



rather on a logical multiplication of them so that having many possi- 

 bilities in mind we are better prepared to direct our attention to what 

 others have never thought of as within the field of possibility. 



Guided by an acute surmise founded on the Rutherford-Bohr 

 quantum theory of the nuclear atom, Moseley contrived a particular 

 juxtaposition of equipment: a discharge tube, a series of substances 

 to be put in that tube, a spectrometer containing a photographic 

 plate, etc. These components were assembled for the sole purpose of 

 obser\ing what was in fact found: a simple relation between the 

 position of blackening on the plate and the identity of the substance 

 present in the discharge tube. Something more than a purely empiri- 

 cal genius diflFerentiates the few like Moseley from the many plodders 

 who never make any such important discoveries. Beyond knowing 

 how to measure, he knew also what to measure. 



If I err in my selection of relevant variables, a fluctuation of my 

 results may alert me to my error; but if I err in my choice of ob- 

 servables no such indication is vouchsafed me. I simply fail to make 

 headway with my problem— which failure may indeed stimulate, 

 though it cannot supply, the creation of some new hypothesis that 

 directs my attention to hitherto neglected observables. No pat for- 

 mula for success is to be found in systematic selection of observables 

 quantitati^'ely determinable. Measurement is not co-extensive with 

 science: measurement is but a tool of science and, though often a 

 notably powerful tool, sometimes one entirely inappropriate. Stephen 

 Hales, highly talented scientist and con\dnced practitioner of the 

 quantitative method— made hundreds of meticulous measurements of 

 tlie volumes of gases released from various specimens. Never did he 

 sense the much deeper significance of the qualitative differences 

 easily demonstrable in these gases— which included such still "un- 

 disco\ered" species as oxygen and hydrogen. A more profound in- 

 sight was won only when, bringing to bear only the very crudest of 

 tests, Priestley and others demonstrated the highly distinctive chemi- 

 cal properties of certain of Hales' specimens of "air." 



Today superior theories pro^'ide superior bases for choice of signif- 

 icant obser\^ables. In any genuinely pioneering study, however, that 

 choice is alwavs and una\oidablv hazardous. In Fermi's classic in- 

 vestigation of the interaction of neutrons with uranium, for example, 

 he noted a product he identified as radium. Only the flimsiest experi- 



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