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land passed by here. It is all the same to me, for he will not pass 

 this way again." 



We all know that there are good and bad experiments. The latter 

 accumulate in vain. Whether there are a hundred or a thousand, 

 one single piece of work by a real master by a Pasteur, for example 

 will be sufficient to sweep them into oblivion. Bacon would have 

 thoroughly understood that, for he invented the phrase experimentum 

 cruets; but Carlyle would not have understood it. A fact is a fact. 

 A student has read such and such a number on his thermometer. He 

 has taken no precautions. It does not matter; he has read it, and if 

 it is only the fact which counts, this is a reality that is as much 

 entitled to be called a reality as the peregrinations of King John 

 Lackland. What, then, is a good experiment? It is that which 

 teaches us something more than an isolated fact. It is that which 

 enables us to predict, and to generalize. Without generalization, pre- 

 diction is impossible. The circumstances under which one has op- 

 erated will never again be reproduced simultaneously. The fact ob- 

 served will never be repeated. All that can be affirmed is that under 

 analogous circumstances an analogous fact will be produced. To pre- 

 dict it, we must therefore invoke the aid of analogy that is to say, 

 even at this stage, we must generalize. However timid we may be, 

 there must be interpolation. Experiment only gives us a certain num- 

 ber of isolated points. They must be connected by a continuous line, 

 and this is a true generalization. But more is done. The curve thus 

 traced will pass between and near the points observed; it will not 

 pass through the points themselves. Thus we are not restricted to 

 generalizing our experiment, we correct it; and the physicist who 

 would abstain from these corrections, and really content himself with 

 experiment pure and simple, would be compelled to enunciate very 

 extraordinary laws indeed. Detached facts cannot therefore satisfy us, 

 and that is why our science must be ordered, or, better still, general- 

 ized. 



It is often said that experiments should be made without precon- 

 ceived ideas. That is impossible. Not only would it make every 

 experiment fruitless, but even if we wished to do so, it could not be 

 done. Every man has his own conception of the world, and this he 

 cannot so easily lay aside. We must, for example, use language, and 

 our language is necessarily steeped in preconceived ideas. Only they 

 are unconscious preconceived ideas, which are a thousand times the 

 most dangerous of all. Shall we say, that if we cause others to inter- 

 vene of which we are fully conscious, that we shall only aggravate the 

 evil? I do not think so. I am inclined to think that they will serve 

 as ample counterpoises I was almost going to say antidotes. They 

 will generally disagree, they will enter into conflict one with another, 

 and ipso facto, they will force us to look at things under different 



