J(, INTRODUCTORY LECTURE ON EXPERIMENTAL PHYSICS. 



It is not till we attempt to bring the theoretical part of our training into 

 contact with the practical that we begin to experience the full effect of what 

 Faraday has called "mental inertia" not only the difficulty of recognising, 

 among the concrete objects before us, the abstract relation which we have 

 learned from books, but the distracting pain of wrenching the mind away from 

 the symbols to the objects, and from the objects back to the symbols. This 

 however is the price we have to pay for new ideas. 



But when we have overcome these difficulties, and successfully bridged over 

 the gulph between the abstract and the concrete, it is not a mere piece of 

 knowledge that we have obtained : we have acquired the rudiment of a perma- 

 nent mental endowment. When, by a repetition of efforts of this kind, we have 

 more fully developed the scientific faculty, the exercise of this faculty in detecting 

 scientific principles in nature, and in directing practice by theory, is no longer 

 irksome, but becomes an unfailing source of enjoyment, to which we return so 

 often, that at last even our careless thoughts begin to run in a scientific 

 channel. 



I quite admit that our mental energy is limited in quantity, and I know 

 that many zealous students try to do more than is good for them. But the 

 question about the introduction of experimental study is not entirely one of 

 quantity. It is to a great extent a question of distribution of energy. Some 

 distributions of energy, we know, are more useful than others, because they are 

 more available for those purposes which we desire to accomplish. 



Now in the case of study, a great part of our fatigue often arises, not 

 from those mental efforts by which we obtain the mastery of the subject, but 

 from those which are spent in recalling our wandering thoughts ; and these 

 efforts of attention would be much less fatiguing if the disturbing force of 

 mental distraction could be removed. 



This is the reason why a man whose soul is in his work always makes 

 more progress than one whose aim is something not immediately connected with 

 his occupation. In the latter case the very motive of which he makes use to 

 stimulate his flagging powers becomes the means of distracting his mind from 

 the work before him. 



There may be some mathematicians who pursue their studies entirely for 

 their own sake. Most men, however, think that the chief use of mathematics 

 is found in the interpretation of nature. Now a man who studies a piece of 

 mathematics in order to understand some natural phenomenon which he has 



