March 7, 1913] 



SCIENCE 



357 



water molecules ai-e flying off into the air 

 and back from the air into the water. But 

 under these conditions more molecules fly 

 from water into air than the reverse ; hence 

 the water gradually disappears from the 

 dish. Heat is nothing but molecular ki- 

 netic energy. If the water is heated, evi- 

 dently the kinetic energy of the water 

 molecules is increased. They therefore dis- 

 appear into the air more rapidly than be- 

 fore, and the dish dries up more quickly. 

 If a bell jar be placed over the dish of 

 water, the molecules of water can not 

 spread over the entire room, but are con- 

 strained to butt their heads against the jar. 

 We should expect these impacts to produce 

 a pressure on the inner walls of the jar. 

 After a time a condition is reached in 

 which just as many molecules fly from the 

 water into the air as fly from the air into 

 the water. Then evaporation should cease. 

 We find that it does so. Under these con- 

 ditions the water vapor in the jar is said 

 to be saturated. 



This second method of teaching thus 

 seeks to interpret phenomena to beginners 

 not in terms of immediate concepts like 

 wet, dry, pounds, inches, pressure and the 

 like, but in terms of less immediate abstract 

 concepts like molecules, atom, imponder- 

 able ether, and so on. Here, again, the 

 effort is made to impress on the pupils 

 conceptions and interpretations which may 

 be wholly concrete to specialists in physics, 

 but which are totally abstract to beginners, 

 especially those of school age. For this 

 reason this type may be called the theoret- 

 ical or abstract method. 



It will be noted that this theoretical or 

 abstract method has much in common with 

 the encyclopedic philosophy, especially as 

 regards method of presenting topics. It is 

 of necessity didactic in spirit, since it pro- 

 poses to impose on the pupils, not the laws 

 and principles of physics, but a survey of 



the whole field, consisting in the last an- 

 alysis of the theories and working hypoth- 

 eses of physics. It, therefore, does not en- 

 courage originality, initiative and creative 

 imagination, since the system which it 

 seeks to implant has already been worked 

 out by the masters and is so comprehensive 

 that the pupils have to be crowded in order 

 to cover it all in the allotted time. The 

 pupils are thus very apt to pick up the 

 terminology of the system long before the 

 terms stand for anything really concrete 

 to them and they use this terminology 

 freely to cover up their real ignorance of 

 how best to control the forces of nature 

 under a given set of real conditions. 



In the courses of this type you will sel- 

 dom find a topic introduced by a daily 

 experience or by a problem that arises from 

 daily experience. These, to the pupils real 

 and concrete things, are usually placed last 

 under the head of applications. You will 

 often find in these courses topics intro- 

 duced by laboratory or lecture experi- 

 ments ; but most of these are, for beginners, 

 little less abstract than the dynes, atoms 

 and unit poles into which they are deftly 

 resolved by the teacher. A thing is not 

 concrete to a pupil merely because it is 

 made of matter ; it is concrete only when it 

 easily associates itself with the concepts 

 and ideas already present in his mind as 

 the result of his previous experiences. 



The abstract philosophy has developed 

 courses that are better organized than the 

 older courses, in that they possess greater 

 unity. They suffer, nevertheless, from 

 many of the faults of the former because 

 they overemphasize the value of physical 

 theory to beginners, and so seek to impose 

 a ready-made system on the pupils without 

 justifying this procedure in advance. 

 Whatever advantages this method may be 

 supposed to have in preparing pupils for 

 later work in some colleges and technical 



