18 Prof. Oliver Lodge on 



clock-weight has somewhat the same function as the string 

 of a bow ; it was the convenient means of generating the 

 potential energy, and it is the means of communicating it to the 

 thing to be driven, but it is not itself energetic, any more than 

 the chain and ratchet-wheel which helped to wind it up were 

 energetic. Or, to take another example, it is like the piston 

 of an air-gun : without it the gas would not have been com- 

 pressed, and it might be (though it is not usually) employed 

 to let the pressure reversibly down again, but it is not itself 

 an active agent either in the charge or the discharge. It is 

 like a Holtz machine or a dynamo : needful to the charging 

 of Leyden jars or storage-cells, but not in itself doing the 

 work, either when used for charging or, when running as a 

 motor, for discharging. 



I fear I am explaining elementary matters at some length ; 

 but, although elementary in one sense, they are not quite 

 easy to seize by the right end ; and the fact that they are so 

 elementary tends actually to retard their apprehension, for 

 unless people have patience to think them out they will not 

 grasp what is meant. The difficulty in all these matters is 

 that everybody thinks he understands them already, and is 

 quite satisfied with his own prehistoric way of regarding them. 

 Now I want to say that I have thought these things out with 

 some care and labour ; and I believe that although no doubt 

 everybody does understand them sufficiently for practical pur- 

 poses, yet, if anyone has faith and patience enough to consent 

 to reconsider them from my point of view (assuming, of 

 course, as in most cases 1 safely may, that it is not his 

 already), he will sooner or later realize the advantage of 

 it. This belief may be presumptuous, but if so I am willing 

 to presume to that extent. 



With the substance of the following quotation from 

 Professor MacGregor, on p. 138, February Phil. Mag., I 

 entirely agree. 



" If there be actions in nature which are not actions at 

 constant distance " [i. e. practically contact-actions] "Prof. 

 Lodge's law is not applicable to them, while the ordinary law 

 is. Even if it be admitted that all actions in nature are 

 contact-actions, there are many groups of phenomena which, 

 in the present state of our knowledge of them, cannot be 

 investigated on the hypothesis of contact-action. The early 

 stages of their investigation must be conducted by the aid of 

 the fiction of action at a distance ; and in such stages Prof. 

 Lodge's law is not applicable, while the ordinary law is. 

 Hence Prof. Lodge's law is not so general in its applicability 

 as the ordinary law/' 



I might prefer to express it differently : I would say that it 



