58 



ORGANIC FUNCTIONING 



a magnetized steel bar, but in the neighbourhood of such a magnet 

 a compass needle is deflected ; this neighbourhood is the seat 

 of a field of magnetic force ; 



Round a wireless station receiving sets are aflpected and respond ; 

 in this neighbourhood there is an electro-magnetic field of 

 force ; 



Round the earth there is a gravitational field (but this is not 

 of the same nature as magnetic or electro-magnetic fields. In 

 the neighbourhood of massive bodies other things that have 

 mass move in certain ways. 



Let the circle E in the following diagram represent an electric- 

 ally charged body : 



\ 



Fig. 1 6. — Diagram of a Field of Force. 



The electric charge is not only on the body, but it also exists 

 all round it to an indefinitely great distance. The concentric 

 circles 1-7, represent imaginary boundaries in this field of electro- 

 static force. At 7 there is a body, E, carrying a small test 

 charge : if we move e from, say, 7 to 5 work is done upon it. 

 The quantity of this work measures the intensity of the charge 

 on E, as it is experienced at e. The intensity of the field 

 decreases as we pass outwards from E, for the charge is always 

 being distributed over an increasingly great region. 



It *' takes time " to build up such a field of force. If E were 

 to be suddenly discharged the field would " collapse " sooner 

 at, say, 5 than it does at 7. Therefore afield of force has extension 

 both in space and time. 



iSb, Oscillators. In many systems the intensity of the 

 included energy regularly decreases and increases, or undergoes 

 regularly repeated transformations. Thus a " Hertzian oscilla- 

 tor " is two spheres near each other and charged with electricity 

 up to sparking-point (the field round them is no longer electro- 

 static). Consider the events : 



