The change of frequency (dn) for a series of lines which behave similarly is approximately proportional to the frequency (n) so that we can take the fraction do/n as a measure of the shift.
Then dn / dt = (b − d ). let r = b − d.
Let V i and V2 be the potentials at points just outside and inside the surface dS, and let n l and n 2 be the normals to the surface dS drawn outwards and inwards; then - dV i /dn i and - dV 2 dn 2 are the normal components of the force over the ends of the imaginary small cylinder.
Then dn / dt = (b − d). Let r = b − d.
