OT: Alien Media (was Disasters and Recovery)

From: Philip.Belben_at_pgen.com <(Philip.Belben_at_pgen.com)>
Date: Fri Jan 22 06:36:18 1999

>> Really? The meter is defined (certain frequency of light from a
certain
>> element for so many waves yada yada). Sea level is defined (don't know
the
>> SI unit, but 780 millibars of pressure). Celcius is defined (0 is
freezing
>> point of pure water at sea level, 100 boiling point of pure water at sea
>> level) and that's all you need to define the gram: one cubic centimeter
of
>> water at 4C at sea level. That also gets you volume (liters).
>>
> I thought length, mass (Kilogram), and time (seconds) were picked as the
> basic SI units, and others, like temperature, were "secondary". For
> electromagnetics,
> a 4'th unit was required, sometimes an ampere (which can be defined from
> mechanical variables), sometimes charge.
> -Dave


In 1902, when the system was proposed, the base units were indeed metre,
kilogram and second. The IEC recommended that the ampere be added as the
fourth unit, and this was finally standardised in 1948.

SI now has seven base units:

Metre, Kilogram, Second, Ampere, Kelvin, Mole and Candela (normally used
without initial capitals btw).

There are two supplementary units, the radian and the steradian.

All other units are derived from these.

Philip.
Received on Fri Jan 22 1999 - 06:36:18 GMT