Development of the formulae of electromagnetism in the M.K.S. system

The use of metres, kilogrammes, amperes, etc., instead of centimetres, grammes, deca-amperes (the C.G.S. unit of current), etc. need not change the method of teaching electricity and magnetism, for it does not interfere with the notions of magnetic poles and point charges of electricity. A logical method of developing the theory from conventional experiments on the forces between magnets, between magnets and current-carrying loops, and between electric charges, is to proceed from magnetic poles to magnetic shells and from these to loops of current, and then bring in the definition of the ampere to evaluate the magnetic constant; consideration of the forces between electric charges follows and, together with identification of rate of change of charge and electric current, leads to the law of induction, to Maxwell´s equations, and to wave propagation, which, in conjunction with the known velocity of light, gives the value of the electric constant. The theory is then extended to material media. A treatment suitable for beginners is outlined in Section 9.