June 18, 1909] 



SCIENCE 



957 



of the physics course to train in scientific 

 thinking seems to me to lie in the fact that 

 the method of presentation nsed is thor- 

 oughly unscientific. Abstract and difficult 

 concepts in the form of definitions and laws 

 are thrust upon the student without warn- 

 ing, and before his mind is adequately pre- 

 pared for them by suitable common sense 

 discussions of his concrete experiences— he 

 does not feel their necessity or see their 

 use. 



Illustrations of this failing may be taken 

 from any chapter of any of the texts now 

 in use. Thus, the discussion of light is 

 generally introduced by statements con- 

 cerning the luminiferous ether; properties 

 of matter are introduced in terms of mole- 

 cules and atoms; heat is explained as a 

 form of energy before its properties are 

 studied. But the most notorious offenses 

 against the scientific spirit of the student 

 are committed in the name of the absolute 

 system of units; they cluster about that 

 tiny and apparently inoffensive thing, the 

 dyne. Unless a student gets a clear con- 

 ception of what a dyne is, he is lost; be- 

 cause most of mechanics depends on it, in 

 the present method of presenting the sub- 

 ject. Far be it from me to attempt to be- 

 little the dyne— it is little enough already. 

 Nor would I give the impression that the 

 dyne is unessential for the adult physicist, 

 or that the absolute units are not the most 

 beautiful and useful of all the "absolutes" 

 under which the rationalistic mind has 

 sought to hide its real ignorance of reality. 

 The trouble with the dyne in elementary 

 teaching is that it can not be derived di- 

 rectly from experience. It depends for its 

 definition on a convention that can not be 

 verified by experience. The student can, 

 of course, learn to recite the definition of 

 the dyne, or even to write the formula that 

 expresses this definition; and, by mechan- 

 ical substitution in this formula, he may 

 be able to solve abstract problems— prob- 



lems that are made up to be problems, but 

 that can not be realized in practise or re- 

 lated to experience. He can not visualize 

 the dyne, nor form a concrete image of it — 

 an image that is derived directly from ex- 

 perience and that is therefore usable in 

 clear thinking. 



To a beginner pushes and pulls are the 

 real forces. He can appreciate their meas- 

 urement by elastic springs, and their com- 

 parison in terms of pounds or grams 

 weight. He can not, as a rule, appreciate 

 the measurement of force in terms of mass- 

 acceleration for three reasons, namely: (1) 

 He has no clear scientific concept of mass 

 and it takes considerable time to acquire it. 

 How many of us teachers would agree on 

 any one attempted definition of mass? (2) 

 He has very imperfect notions of accelera- 

 tion ; and he really can not get a concrete, 

 quantitative picture of this without the 

 calculus. Did not Newton himself invent 

 the calculus before he was able to treat 

 acceleration? (3) In all of his actual ex- 

 periences with natural phenomena the force 

 balanced by mass-acceleration is small com- 

 pared with the force balanced by friction 

 and other resistances. 



For these reasons it seems to me per- 

 fectly clear that the dyne should not be 

 introduced at the beginning of a course in 

 elementary physics. If a second year of 

 work in this subject is given in the high 

 school, the dyne might be introduced then, 

 provided that the first course had been of 

 the right sort ; otherwise it must be left for 

 the colleges. 



Since the dyne is the actual point of con- 

 tact—I might appropriately say the mathe- 

 matical point of contact — between the two 

 opposing pedagogical creeds of physicists, 

 it is very important that we see the point 

 clearly and appreciate its great significance 

 for physics teaching. I, therefore, will 

 adduce some of the arguments that are put 

 forth in favor of retaining the dyne so as 



