HYPOTHESIS 123 



planets, or the phenomena of the refraction and reflexion of 

 light we may conceive and verify hypotheses as to the exact 

 quantitative relations between those various elements and motions, 

 without for the time inquiring either into their origin or their 

 raison ctetre, their efficient or their final causes. We may, by 

 accurate observation and experiment, seek to arrive at an exact 

 quantitative expression of the various events and agencies which 

 make up the whole phenomenon. We may aim, in other words, 

 at weighing and measuring the facts, at describing them with 

 mathematical precision, at establishing formulae which will be 

 &quot; descriptive statements of the exact character of the phenomena 

 to be explained, when their relations to other phenomena are 

 not in question &quot; ; * at reaching expressions which will describe 

 concisely and accurately the quantitative side of those phenomena. 

 Now, the scientist s supposition or conjecture as to the exact 

 quantitative relation or ratio between some or all of the various 

 elements or motions in a given series of phenomena, has been 

 commonly called an Hypothesis of Law. And when such sup 

 position is verified, and formulated in clear and concise language, 

 it is what is commonly recognized in the physical sciences as a 

 Physical Law. A &quot; law &quot; of nature, in this sense of the term, 2 

 tells us &quot;how&quot; a phenomenon takes place, i.e. in what exact 

 measure and proportion the various constituent agencies and 

 energies must be present and operative ; it is simply an exact 

 mathematical description of the measure in which a certain 

 phenomenon regularly occurs. Such, for example, are the &quot; laws &quot; 

 of refraction and reflexion of light ; or the &quot; law &quot; which states 

 that the strength of an electric current varies directly as the 

 electromotive force and inversely as the resistance of the circuit ; 

 or the &quot;law&quot; of gravitation, that any two bodies in the universe 

 tend to move towards each other with an acceleration that varies 

 directly as the product of their masses and inversely as the 

 square of their distance apart : &quot; The business of physical 

 science,&quot; writes Mach, &quot; is . . . the abstract quantitative expres 

 sion of facts. The rules which we form . . . [for this purpose] 

 ... are the laws of nature.&quot; 3 



But though this mathematical measurement of phenomena 

 gives us a clearer description of them, still it does not give us a 



1 WELTON, Logic, vol. ii., p. 91. 



&quot;For another and deeper sense of this expression, see above, 217. 



*apud WELTON, loc. cit. 



