unresolved questions

["Thomas H. Hogan" <flzhgn@xxxxxxxxxxxxx>]

Well, I can't resist taking a turn at these questions:
>... there are the iron pictures made on IR film that do show the
>heat.  And, as discussed here earlier, whether a given wavelength
>should be considered as heat depends on what materials we're talking
>about.  Anyone have any further thoughts on whether it might be
>possible--using a long exposure at night, no doubt--to actually
>photograph heat loss on HIE?
Maybe it will help to think about heat as electromagnetic radiations of 
substances.  Hot substances radiate heat right?  Some of that heat
radiation has short enough wavelength to cause a change in the silver
halide crystals of HIE film (actinic radiation) but most of the heat
radiation is too long in wavelength to induce the change (of electron
orbitals in sensitized silver halides)in film to expose it (so called
caloric radiation).  Now think of those hot irons as emitting heat
energy
that has a wavelengths distributed in bell shaped curve--the hotter the
irons the more the bell shaped curve (Gaussian distribution) moves 
toward the actinic side of the electromagnetic spectrum.
  Is this any help?   Anyway somethings can be heated sufficiently to
emit enough actinic infrared radiation to expose HIE film in long
exposures,
yet still remain invisible to the vertebrate eye in total darkness.
If you can't get absolute darkness then use a Wratten #87 to block stray
light.

>More recently I raised a question (and got one specific wrong) on a
>peculiarity of certain pigments that I don't understand.  I once had a
>lot of old lacquer recording blanks that I had to strip to send the
>aluminum substrates off for what today we'd call recycling.  I
>discovered that when you looked through a single layer of the lacquer,
>it looked sort of a characterless blue color.  But when I doubled the
>thickness to two layers it looked deep red (very much like a Wratten
>29), and when I increased the number of layers above two, the red got
>progressively deeper, but only gradually.
Well, there may be a wee bit 'o blue in that lacquer, Laddy, tha'd be
absorbed by the red in it.

  Similarly, there are bulbs
in the New York subway tunnels that play a similar trick.  At a
distance, you see a ruby red glint, but when you get close it turns
out to be a blue bulb.  (That's what I got wrong--I had near and far
conditions reversed.  And I don't know what the bulbs are there for.)

Some people put little blue bulbs inside the red tailights of
automobiles
when you see these at a great distance on the freeway they are not so 
remarkable but when you get closer they definitely look a wonderful 
purple color!  It's one of my favorite sites driving on the California 
freeways at night.  I'm not sure what is going on here, but blue light
is scattered by oxygen (Rayleigh effect). By the way, liquid oxygen has
the most spectacular sky blue color!  It looks like liquid sky when it
is poured from a Dewar flask! --  Perhaps there is something
similar but it could be due to lenses and refraction of red vs blue
light.  If you wear yellow lenses (many mammals are naturally equipped
with yellow lenses) you can't see the blue !

>I'd be interested in any explanation of these two phenomena.

Bob Long
(boblong@xxxxxxxxxxx)

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Topic No. 6