Septembek 24, 1915] 



SCIENCE 



403 



may be sound in reasoning ? It can only do 

 so because every problem involves a much 

 larger number of conditions than those 

 which the investigator can take into ac- 

 count. He therefore rejects those which he 

 believes to be ^inessential, and if his judg- 

 ment is at fault he goes wrong. But the 

 practical man will often fail for the same 

 reason. When not supported by theoretical 

 knowledge he generalizes the result of an 

 observation or experiment, applying it to 

 cases where the result is determined by an 

 altogether different set of conditions. To 

 be infallible the theorist would have to take 

 account of an infinite number of circum- 

 stances, and his calculations would become 

 unmanageable, while the experimenter 

 would have to perform an infinite number 

 of experiments, and both would only be able 

 to draw correct conclusions after an infinite 

 lapse of time. They have to triist their 

 intuition in selecting what can be omitted 

 with impunity, and, if they fail, it is mainly 

 due to the same defect of judgment. And 

 so it is in all professions: failure results 

 from the omission of essential considera- 

 tions which change the venue of the prob- 

 lem. 



Though theory and practise can only 

 come into opposition when one of them is at 

 fault, there is undoubtedly a contrast in 

 character and temperament between those 

 who incline more towards the one and those 

 who prefer the other aspect: some like a 

 solitary life at the desk, while others enjoy 

 being brought into contact with their fel- 

 lows. There have at all times been men 

 predestined by nature to be leaders, and 

 leadership is required in all branches of 

 knowledge — the theoretical as well as the 

 more active pursuits; but we must guard 

 against accepting a man's estimate of his 

 own power to convert his thoughts into acts. 

 In the ordinary affairs of life a man who 

 calls himself a man of action is frequently 



only one who can not give any reasons for 

 his actions. To claim that title justly a 

 man must act deliberately, have confidence 

 in his own judgment, sufficient tenacity of 

 purpose to carry it through, and sufficient 

 courage to run the unavoidable risks of 

 possible failure. These risks may be trivial 

 or they may be all-important. They may 

 affect the reputation of one unit of crea- 

 tion or involve the whole life of a nation, 

 and according to the greatness of the issue 

 we shall honor the man who, having taken 

 the risk, succeeds. But whether the scale 

 be microscopic or interstellar, the essence of 

 the faculty of blending theory and practise 

 is the same, and both men of books and men. 

 of action are to be found in the philosoph- 

 er 's study and the laboratory, as well as in 

 the workshop or on the battlefield. Modern 

 science began, not at the date of this or that 

 discovery, but on the day that Galileo de- 

 cided to publish his Dialogues in the lan- 

 guage of his nation. This was a deliberate' 

 act destined to change the whole aspect of 

 science which, ceasing to be the occupation 

 of a privileged class, became the property 

 of the community. Can you, therefore, 

 deny the claim of being a man of action to 

 Galileo, can you deny it to Pasteur, Kelvin, 

 Lister, and a host of others ? There are, no 

 doubt, philosophers who can not manage 

 even their own affairs, and whom it would 

 be correct to call pure theorists, but that 

 proves nothing, because their defect makes 

 them worse philosophers as well as worse 

 citizens. 



In his Presidential Address, delivered to 

 this association in 1899, Sir Michael Foster 

 summarized the essential features of the 

 scientific mind. Above all other things he 

 considered that its nature should be such as 

 to vibrate in unison with what it is in search 

 of; further, it must possess alertness, and 

 finally moral courage. Yet after enumera- 

 ting these qualities, he arrives at the same 



