"Nick Maclaren" wrote in message
...
In article ,
Franz Heymann wrote:

[On reradiation]
No, what I mean is surface heating. This is the effect by which
the
surface of an object can become much hotter than either the body
of
the object or the air temperature.

Which of the objects under the glass will receive more reradiated
heat
from neighbouring bodies than others?

Those that are an approximation to a focus of the glass structure.

There is no such thing as "focus of the glass structure". Each light
ray exits from the glass at the same angle as that a which it entered.
At worst, it might be displaced sideways parallel to its original
trajectory by a millimetre or two. The intensity distribution is then
essentially the same as it would have been if there had been no glass.

Are you remembering that the body you have chosen to receive
reradiated heat is itself also reradiating?

Of course.

Surely as time passes, all the objects in the enclosure will try to
achieve the same temperature?

Er, no. That is FAR too simplistic a model.

Err, no.

Remember that there
is an external source of energy, and therefore the most elementary
steady state calculations do not apply.

I know that. I am almost right. The short term temperature of each
body in it will depend essentially only on its albedo. The various
plant leaves will have very nearly equal albedos.

One point is that glass reflects
long (far) wavelength infrared well,

That is not true. It absorbs infrared radiation.

Please go and look it up.

I suggest you do that. Glass absorbs infrared quite strongly, which
is why infrared lenses have to be made of rather unusual materials,
many of which are in fact black as far as visible light is concerned.

The greenhouse effect is precisely that
the short wavelength infrared emitted by the sun is transmitted,
but the long infrared emitted by the earth is reflected.

No. You misunderstand the greenhouse effect quite seriously.

Yes,
they are both absorbed, too, but everything is relative.

You seem to be unaware of the fact that there is a relationxsship
between the reflection coefficient and the absorption coefficient of
any optical medium. A good absorber is a bad reflector, and glass is
a very good absorber of infrared radiation.

The greenhouse effect arises in fact because the glass absorbs
essentially all the reradiated infrared quite close to the inner
surface of the glass, whose temperature rises as a consequence. Most
of this heat is returned to the enclosed volume by convection and
reradiation.

Franz