Die hebben het perpetuüm mobile uitgevonden. Gewoon lucht insluiten en het wordt helemaal vanzelf warm
Je snapt best wat ze proberen te zeggen. Hieronder het experiment beschreven, waarbij het gaat om het feit dat de lucht niet of nauwelijks extra verwarmd wordt door absorbtie.
2.5 Experiment by Wood
Although the warming phenomenon in a glass house is due to the suppression of convection,
say air cooling10, it remains true that most glasses absorb infrared light at wavelength 1 m
and higher almost completely.
An experimentum crucis therefore is to build a glass house with panes consisting of NaCl
or KCl, which are transparent to visible light as well as infrared light. For rock salt (NaCl)
such an experiment was realized as early as 1909 by Wood [109{112]:
There appears to be a widespread belief that the comparatively high temperature
produced within a closed space covered with glass, and exposed to solar radiation,
results from a transformation of wave-length, that is, that the heat waves from
the Sun, which are able to penetrate the glass, fall upon the walls of the enclosure
and raise its temperature: the heat energy is re-emitted by the walls in the form
of much longer waves, which are unable to penetrate the glass, the greenhouse
acting as a radiation trap.
I have always felt some doubt as to whether this action played any very large part
in the elevation of temperature. It appeared much more probable that the part
played by the glass was the prevention of the escape of the warm air heated by
the ground within the enclosure. If we open the doors of a greenhouse on a cold
and windy day, the trapping of radiation appears to lose much of its ecacy. As a
matter of fact I am of the opinion that a greenhouse made of a glass transparent
to waves of every possible length would show a temperature nearly, if not quite,
as high as that observed in a glass house. The transparent screen allows the solar
radiation to warm the ground, and the ground in turn warms the air, but only
the limited amount within the enclosure. In the open", the ground is continually
brought into contact with cold air by convection currents.
To test the matter I constructed two enclosures of dead black cardboard, one
covered with a glass plate, the other with a plate of rock-salt of equal thickness.
The bulb of a thermometer was inserted in each enclosure and the whole packed
in cotton, with the exception of the transparent plates which were exposed. When
exposed to sunlight the temperature rose gradually to 65 C, the enclosure covered
with the salt plate keeping a little ahead of the other, owing to the fact that it
transmitted the longer waves from the Sun, which were stopped by the glass. In
order to eliminate this action the sunlight was rst passed through a glass plate.
There was now scarcely a di erence of one degree between the temperatures of the
two enclosures. The maximum temperature reached was about 55 C. From what
we know about the distribution of energy in the spectrum of the radiation emitted
by a body at 55 C, it is clear that the rock-salt plate is capable of transmitting
practically all of it, while the glass plate stops it entirely. This shows us that the
loss of temperature of the ground by radiation is very small in comparison to the
loss by convection, in other words that we gain very little from the circumstance
that the radiation is trapped.
Is it therefore necessary to pay attention to trapped radiation in deducing the
temperature of a planet as a ected by its atmosphere? The solar rays penetrate
the atmosphere, warm the ground which in turn warms the atmosphere by contact
and by convection currents. The heat received is thus stored up in the atmosphere,
remaining there on account of the very low radiating power of a gas. It seems to
me very doubtful if the atmosphere is warmed to any great extent by absorbing
the radiation from the ground, even under the most favourable conditions.
I do not pretend to have gone very deeply into the matter, and publish this note
merely to draw attention to the fact that trapped radiation appears to play but a
very small part in the actual cases with which we are familiar."