54 POPULAR SCIENCE MONTHLY. 



to nature is made but once and at the start, in physics new appeals 

 to experience must often be made in the course of the reasoning, and 

 the final relations are accepted only when they are not contradicted 

 by the order of nature. And sometimes, even if the facts do not 

 support the theory, it is still important to observe that the conditions 

 of experiment may not have been so simple as the premises assumed and 

 that the theory may still be true when the proper limitations are intro- 

 duced. In the minds of certain men who are pleased to call themselves 

 practical, a theory is exploded and to be completely rejected as soon 

 as any discrepancy appears between the observed facts and the reasoned 

 conclusions. To the physicist, however, some sort of theory or rational 

 guide is so important and even necessary that a very imperfect or in- 

 sufficient theory is preferable to none at all. He is not one of those 

 who delight to hold up to ridicule false and abandoned theories, of 

 which so many examples may be found in the history of physics, for he 

 truly recognizes that though they now seem absurdly wrong, they 

 nevertheless served a useful purpose as a temporary scaffold, without 

 whose aid the more lasting structure might never have been erected. 

 From familiar acquaintance with the imperfections of all experimental 

 data, the physicist grows into the habit of holding his deductions sub- 

 ject to correction in the light of new or more accurate observations. 

 Thus there arises the idea so well expressed by the late Professor 

 Eowland, of degrees of truth or untruth. 



There is no such thing as absolute truth and absolute falsehood. The 

 scientific mind should never recognize the perfect truth or the perfect false- 

 hood of any supposed theory or observation. It should carefully weigh the 

 chances of truth and error and grade each in its proper position along the 

 line joining absolute truth and absolute error. 



The ordinary crude mind has only two compartments, one for truth and one 

 for error; indeed the contents of the two compartments are sadly mixed in 

 most cases; the ideal scientific mind has an infinite number. Each theory or 

 law is in its proper compartment indicating the probability of its truth. As 

 a new fact arrives the scientist changes it from one compartment to another 

 so as if possible to always keep it in its proper relation to truth and error. 



The aim of physical science, according to the earlier writers, was 

 the explanation of the phenomena of nature, i. e., the tracing of 

 occurrences to their causes or the proceeding by logical advance from 

 the cause to the effect. The modern and more acceptable view, due 

 perhaps in large measure to Kirchhoff, is that science aims to state 

 in simple and easily reproducible language the order of the processes 

 of nature. A phenomenon then has received its full explanation when 

 we have presented to the mind a picture or a model in which we may 

 reproduce at will the sequence of events which is observed in nature. 

 All attempts beyond this to satisfy the sense of causation must be futile. 



It is a well-known fact that the mind derives a certain pleasure in 



