Ron Kean wrote:
>
> Every so often, physics tries to purge itself of inconsistency.
> Historical electromagnetic units, for example, come in several systems
> which are unbelievably convoluted and confusing and which make the whole
> subject difficult to understand. Some years ago, the 'International
> System of units' was devised. It is called SI after its French initials.
> In the 1980s, the meter was redefined in terms of the speed of light,
> whereas earlier it had been defined as a certain number of wavelengths of
> a certain spectral line of Krypton 86. The meter is now defined as the
> distance light travels in 1/299,792,458 second. That means we no longer
> have to wonder what is the exact speed of light. It is 299,792,458
> meters per second, exactly, by definition.
Mike Lorrey