i68 THE POPULAR SCIENCE MONTHLY 



extensively used text-book of zoology, written by a biologist of inter- 

 national reputation, occurs this passage: 



An excised representative sample of hydra will reproduce the whole: but you 

 can not perform this experiment with the frog. 



To one who looks upon an experiment as a means of testing hypoth- 

 eses there is no obvious reason why " this experiment " can not be per- 

 formed with a frog, or any other beast. But if the experiment is a 

 means for getting certain desired objective results, of course it is im- 

 possible to get a complete frog to regenerate from an "excised repre- 

 sentative sample " — as we know from experiments ! 



That the experiment does not always mean to the teacher the same 

 as it does to the investigator may be inferred from the fact that many 

 teachers are not averse to "faking" experiments that are arranged for 

 demonstration purposes. William James tells in one of his papers of 

 his own performance in a physiological demonstration, and he justifies 

 it upon pragmatic grounds. The question I am raising is not one of 

 ethics, but of clear thinking. If the experiment is a didactic tool for 

 presenting concrete, objective processes, it falls into the same category 

 as wall-charts and models. The demonstration experiment need not 

 then be any more " real " than a glass model of the eye or of a diamond. 

 But if the experiment is used by the teacher for the purpose of teaching 

 method in thought or in the solution of problems, the " unsuccessful " 

 experiment should be at least as illuminating and educating as the 

 "successful" one. 



A third source of confusion lies in the apparently harmless little 

 word " law." A student of science should certainly know what is meant 

 by a "law of nature" — but we may not expect him to if his teacher 

 does not. Now it is altogether too common to hear teachers of science 

 speak of the laws of nature in exactly the same way as ordinary folks 

 whose notion of " law " is derived from the statutes of the commonwealth 

 or the commandments of the gods. In science a law is presumably a 

 generalization from a limited series of experiential data, not a prohibi- 

 tive or mandatory order from some superior authority. Our attitude 

 toward Boyle's law, for example, is in no way related to our loyalty to 

 Mr. Boyle. In ordinary usage there may be violations of "law" and 

 such violations are frequently followed by disagreeable consequences. 

 But in "nature" the consequence is not something superimposed by 

 way of punishment or retribution; it is itself a part of the law, and 

 integral in the general process formulated in the law. Laws of nature 

 can not be violated in the sense that statutory laws can be. Laws of 

 health are descriptive generalizations of the conditions under which 

 normal health is maintained. Yet we speak of empirical rules for 

 securing these conditions as also being "laws of health." In practise 

 we may or we may not observe these rules ; but we can not violate the 

 laws. Morbid conditions also arise in conformity to law. There is 



