Continuity 19 



known to us; the law is not really dis- 

 obeyed, but is modified through the 

 action of a known additional cause. 

 Hence it is all in the direction of progress. 

 It is only fair to quote Poincare again, 

 now that I am able in the main to agree 

 with him : 



Take for instance the laws of reflection. 

 Fresnel established them by a simple and at- 

 tractive theory which experiment seemed to con- 

 firm. Subsequently, more accurate researches 

 have shown that this verification was but 

 approximate ; traces or elliptic polarisation were 

 detected elsewhere. But it is owing to the first 

 approximation that the cause of these anomalies 

 was found, in the existence of a transition layer; 

 and all the essentials of Fresnel' s theory have 

 remained. We cannot help reflecting that all 

 these relations would never have been noted if 

 there had been doubt in the first place as to the 

 complexity of the objects they connect. Long 

 ago it was said : If Tycho had had instruments 

 ten times as precise, we would never have had a 

 Kepler, or a Newton, or Astronomy. It is a , 

 misfortune for a science to be born too late, when 

 the means of observation have become too per- 

 fect. That is what is happening at this moment 

 with respect to physical chemistry: the founders 



