REFORMS IN THE TEACHING OF ELECTRICITY 529 



battery, using the ammeter and voltmeter which he has cali- 

 brated ; thus Ohm's Law is rediscovered in the form now used by 

 practical men. We then consider the whole circuit and define 

 battery resistance in the same manner as the armature resistance 

 of a dynamo. The way in which we can lead up to absolute 

 C.G.S. units at a later stage of the learner's career will be 

 indicated later on. 



For this course no attempt is made to give from the start a 

 complete conception of electromotive force, potential difference 

 and the distinction between them. The mechanical foundation 

 is not reached at this stage ; the boy is not ready for it but he 

 gets a very clear working idea of electromotive force and 

 potential difference sufficient for his present needs. On the 

 other hand, it is very doubtful whether the ordinary school 

 course of frictional electricity provides this complete conception. 

 Few young boys completely grasp the meaning of a line- 

 integral of electric force or the work done on an imaginary 

 unit charge brought up from infinity. The lack of names for 

 electrostatic units and the impossibility of any simple calcula- 

 tions in the ordinary course of frictional electricity are serious 

 obstacles to the drill needed to force such ideas into a boy. 

 And even if he were to understand it thoroughly, is sufficient 

 stress laid on the identity of frictional and voltaic electricity to 

 make him confident that what he has learnt of electricity in one 

 connexion he can use in the other ? It is customary to show 

 a condensing electroscope or a quadrant electrometer with this 

 object but I suspect that we really trust rather to the fact that 

 the same names are used throughout. 



The other important criticism is that this treatment of 

 Ohm's Law is not logical. Even if it were not rigorous, 

 experience suggests that the teacher's conscience would be the 

 only sufferer; for over-emphasis on logic at that age defeats 

 itself, as teachers of mathematics have recently shown with 

 reference to deductive geometry. So we might confess our- 

 selves better satisfied if we provided a young boy with a vivid 

 conception, based only on such logic as he is fit to understand, 

 than if we pursued a course to which no exception can be 

 taken but which leaves no impression on his mind. As he 

 grows older he can appreciate a more rigorous demonstration, 

 perhaps all the better if the pace was not forced when his mind 

 was too immature for it ; and he has not to unlearn the truth, 



