SCIENCE, YESTERDAY, TODAY, TOMORROW — SWANN 239 



tiling is to say nothing. However, if you are expert in tlie art of 

 oratory, you will be able to say it with force and conviction. 



Let us consider, as an example, a physicist who studies the science 

 of electrodynamics and gravitation separately and later desires to 

 mold them into a common theory. It will be unnecessary for us to 

 think of gravitation in the light of the general theory of relativity. 

 The old Newtonian concept will suffice. 



Our physicist studies the laws of the heavens and finds that they 

 conform very well to the Newtonian law of gravitation. I point out 

 to him that some of the celestial bodies are magnets and that their 

 attractions for one another will be modified in form and degree by 

 this circumstance. The physicist replies quite correctly that the 

 phenomenon is of very small numerical magnitude and that he pro- 

 poses to neglect it. Next day, I find the physicist in his laboratory 

 studying the attraction of magnets and of electrically charged bodies 

 for one another. I point out that these bodies also attract gravita- 

 tionally, and that he should take this into account. Again he replies, 

 quite correctly, that in these experiments the gravitational effects 

 are so small compared with the electromagnetic effects that he is 

 justified in neglecting them. In other words, in one problem of the 

 universe, our physicist neglects the phenomena which are the whole 

 source of interest in another problem, in which other problem, more- 

 over, the phenomena dominant in the first problem are now negligible. 



Now neglect of the small gravitational effects in the electromagnetic 

 experiments is justifiable so long as one maintains the principle that 

 the gravitational effect is, in actuality, there. If the gravitational 

 effect is omitted, even in the formulation of the general principles 

 of the subject, on the basis of its being too small to detect in electro- 

 magnetic experiments, and if the laws of these experiments are, there- 

 fore, placed on the statute books without it, they will possess no 

 power to recognize it in any other phenomena of nature where the 

 circumstances may be different. They will, in fact, be in danger of 

 actually denying its existence in any field whatever, and of rendering 

 its subsequent discovery in the astronomical field a phenomenon 

 puzzling to comprehend, and apparently antagonistic to the science 

 of electrodynamics. 



Now, if a general theory embracing electrodynamics and gravita- 

 tion is provided, it may take care of problems in which gravitational 

 forces and electrodynamical forces are equally important even 

 though nature may present us with no such cases where they are of 

 equal importance. Such a general theory is able to extrapolate itself 

 to one end to a case where gravitation is unimportant and electro- 

 dynamics is all important and to extrapolate itself also to the other 

 end to a case where the relative importance of these respective phe- 



