310 EXPERIMENT STATION RECORD. [Vol. 36 



exercised. And they have made highly important contributions to 

 the knowledge of their day and generation. 



In some respects we have learned how not to know, and have set 

 our faces in the right direction — the direction of making our knowl- 

 edge exact in so far as it goes and as the status of science permits. 

 We have learned not to hesitate to abandon or modify practical and 

 theoretical views on the basis of new light, and so to make our work 

 progressive and constructive by building fact upon fact and sequence 

 upon sequence. 



