2 Prof. Oliver Lodge on 



not one which will bear pressing into individual cases, but if 

 it contains an element of truth it has reference to no personal 

 detail, as it seems to me, but to a difference in type ; and I 

 sometimes think that most minds, except those few of the 

 very highest order who are above classification, may be said 

 to fall into, or at least to lean toward, one or other of these 

 categories*. Each type of mind performs its service, and 

 each type has its appropriate danger. 



The detection of a real complication is a service to truth ; 

 the invention of a needless complexity is a disservice and 

 temporary obstruction. The reduction of apparently complex 

 facts to a simple statement in commonplace language is, I 

 believe, a service ; the over-simple and incomplete summary 

 of what is really complex is not an equal service, but I do not 

 perceive that it is likely to be any serious obstruction : it 

 seems to me rather of the nature of a first approximation, 

 which is often temporarily helpful. 



When Ohm stated his law that current is proportional to 

 E.M.F., he did not know that it was really true. It has 

 turned out to be precisely true for copper and for sulphate of 

 copper — the only substances for which it has been seriously 

 tested ; but even if it had not been so accurate, its statement 

 was a service, since it enabled half a century to walk in the 

 light instead of in the dark. There is no evidence that it is 

 accurately true for every variety of solid and liquid conductor, 

 but by this time it is the fashion to assume its truth in 

 ordinary simple cases. And rightly so, as it seems to me ; the 

 burden of proof rests now with the enterprising experimenter 

 who can detect a flaw in it. His evidence will be listened to, 

 but till it is forthcoming vague doubts can be legitimately 

 ignored. 



Take another example : — The characteristic equation of gases 

 in the simple form pv = RT has done good service, though it 

 turns out to be untrue for every actual substance. Without 

 it, however, we should have been unnecessarily floundering 

 in the dark. Even now it is more used in dealing with gases 



* I see no reason in Dr. MacGregor's book on Dynamics for including 

 him in the first category : it is his Presidential Address on the Laws of 

 Motion that alone suggested it. I do not intend the classification as in 

 any way offensive : I should think that Prof. Karl Pearson, for instance, 

 would willingly enrol himself under the first head rather than under 

 the second, judging by his ' Grammar of Science.' But very likely 

 MacGregor has stated the laws of motion in their simplest conceivable 

 form if attraction and repulsion across a distance are to be contemplated. 

 That is the essential difference between us : he is willing to base 

 Physics on action at a distance ; I am not. From the action-at-a-distance 

 point of view his statements are in many respects admirable, especially 

 those near the conclusion of his essay. The remarks in the text are in- 

 tended to have only a general and impersonal application. 



