Tom Donaly wrote:
If a coil can slow down an electromagnetic wave as much as these
equations say it can, though, it qualifies as a very interesting device.

Tom,

Here's another way to think about it.

If an inductor by itself delayed phase as much as Cecil claims, we
could build a phase or time delay system with only a large inductor. As
it is, we must always use a network of capacitors and inductors to
obtain phase delays or a transmission line of any substantial delay.

To construct a delay line, either a small parallel wire line is used or
a spiral around a metal core. The metal core acts like a shorted turn
and reduces flux coupling, and adds distributed capacitance to ground.

73 Tom