OT: Speed of light [was Re: Why not a Python compiler?]

[Jeff Schwab]

Grant Edwards wrote:
> On 2008-02-13, Jeff Schwab <jeff at schwabcenter.com> wrote:
> 
>>> Eh? Last I checked both pound and kilogram are units of mass, so where is
>>> the incompatibility?
>> I've never heard of "pound" as a unit of mass.  At least where I went to 
>> school (Boston, MA), "pound" is the English unit of force, "slug" is the 
>> (rarely used) English unit of mass,
> 
> Back in the day, I was once working on a fire control system
> for the Navy.  All the units in the calculations were purely
> metric except for one: air density was in slugs/m3.  I always
> suspected that was somebody's attempt at humor.

So what is the mass of a slug, anyway?  (I assume this is slug as in 
bullet, not slimy, creeping thing.)