January 7, 1910] 



SCIENCE 



pleasures." We should keep this always 

 in mind in the presentation of our subject, 

 but should not go so far in our wish to 

 arouse this higher pleasure in the student 

 as to make incorrect statements as the one 

 that the pressure coefficient P is a force, 

 and the other quantity A in our first equa- 

 tion an area. Let us be consistent and use 

 the term "pressure" only for one physical 

 quantity, and not for two or even three. 

 In modern education we find too much a 

 tendency to introduce kindergarten meth- 

 ods in the high schools; keep them out of 

 the college. 



&. In surface-tension phenomena we have 

 a very similar case, since the force is ex- 

 pressed here by the equation 

 F=Tl. 



The capillary constant T is usually 

 called ' ' surface tension, ' ' but we may read 

 in the same book which gives this defini- 

 tion, that the weight of a liquid is balanced 

 by the surface tension. The latter state- 

 ment, though consistent with ordinary 

 usage, does not agree with the former 

 definition. All the preceding arguments 

 in favor of accuracy and unif oi'mity in our 

 teaching apply in this case. 



It is true, it is a hard task to teach stu- 

 dents a new meaning of a word which they 

 have been in the habit of iising in a differ- 

 ent, or at least in a much broader sense. 

 But are we not successful in making them 

 distinguish between mass and weight, 

 though the same difficulty arises in this 

 case? It is well known that the impor- 

 tance of the law of conservation of energy 

 was not fully appreciated, until the new 

 term "energy" with its definite present 

 physical meaning was introduced and we 

 stopped talking about the conservation of 

 force. 



c. In the chapter on Heat we find sev- 

 eral inconsistencies. Every physicist 

 knows perfectly well that the term "ab- 



solute temperature" refers to temperature 

 measured on the thermodynamic scale. 

 Nevertheless, we call the zero of the con- 

 stant volume hydrogen thermometer the 

 absolute zero and we call temperatures, 

 measured from this point and by this 

 thermometer, absolute temperatures. We 

 even refer to any gas thermometer, no mat- 

 ter whether of constant volume or con- 

 stant pressure, in defining absolute tem- 

 perature. There seems to be no other 

 remedy but to invent a new name, a tempt- 

 ing task for a philologically inclined phys- 

 icist. Do not let us make light of our 

 trouble because these different tempera- 

 ture scales agree so very closely. They 

 are different. A man has not discovered 

 the north pole even if he came within a 

 few miles of it. 



d. Another example occurs in the com- 

 mon expression of quantity of heat as 

 E = oM(U — t^). 



The factor c is visually called "specific 

 heat." It is really the "heat capacity of 

 the substance" in question and is taken as 

 unity for water under standard conditions. 

 But it is not a pure number. It has defi- 

 nite dimensions, while "specific heat," de- 

 fined as the ratio of the heat capacity of 

 the substance to that of water, is a pure 

 number; in other words, the relation be- 

 tween these two thermal quantities is ex- 

 actly similar to that between density and 

 specific gravity. We distinguish very 

 carefully between the latter two, even 

 where the numerical value would be the 

 same. 



This numerical equality has done more 

 than anjrthing else to befog our minds 

 about the true nature of a physical quan- 

 tity. Nest in importance comes our in- 

 heritance of terms from old, long dis- 

 carded theories. Think of such terms as 

 "specific heat" which is not heat at all, 

 or "electromotive force" which is no 



