Greenhouse

["Rauber, Joel Phys" <RAUBERJ@mg.sdstate.edu>]

Leigh made the following interesting comment/observation concerning 
greenhouses; and I confess to never having thought about it much.

> I don't think I've harped on it before in this group, but how many
> of you out there are teaching your students that a greenhouse gets
> warm because of the greenhouse effect, the same effect that heats
> planetary surfaces with atmospheres? That's a lie, of course. It
> has been known since the teens that greenhouses are heated by the
> supression of cooling by convection. R. W. Wood (who probably knew
> that all along) proved it by making a test greenhouse out of rock
> salt. Today we use polyethylene sheet for some greenhouses, the
> same material that is used for infrared windows in vacuum apparatus.

I have the following question:  Are not both affects happening 
simultaneously and contributing to the warmth inside the greenhouse (or 
car)? (It doesn't get to hot inside my car on a cloudy day, or at night, up 
here in the upper midwest).  So it strikes me that one should be asking 
which is the predominate affect?

Joel