"an occasional draft will look like a passing cloud"
July 18, 2017 8:30 AM   Subscribe

A demonstration of Schlieren photography, which makes minute changes in air's index of refraction visible, allowing us to see air that is moving or that contains gases that would otherwise be invisible. A segment from a Science Channel program has some additional examples and some explanation.

There's also some background from the Harvard demonstration on how they set this up and how it works.
posted by Copronymus (15 comments total) 45 users marked this as a favorite
 
This is how you visualize shock waves in supersonic wind tunnel testing, among other things.
posted by indubitable at 8:47 AM on July 18, 2017 [1 favorite]


This is amazing!
posted by aubilenon at 9:25 AM on July 18, 2017


I just had a couple of long plane trips this week and it never ceases to trip me out that air is a fluid. We are swimming in air! My 10yo is going to love this.
posted by selfmedicating at 9:55 AM on July 18, 2017 [1 favorite]


We are swimming in air!

First thing I thought of when reading that sentence.
posted by Greg_Ace at 10:39 AM on July 18, 2017 [1 favorite]


Schlieren photography . . .

Oh my god this is actual magic.


Nah, that'd be Kirlian photography.
 
posted by Herodios at 11:39 AM on July 18, 2017 [2 favorites]


Cooool! Thanks for this.
posted by mandolin conspiracy at 1:29 PM on July 18, 2017


Wikipedia link for those interested.

"In classical schlieren photography, the collimated light is focused with a converging optical element (usually a lens or curved mirror), and a knife-edge is placed at the focal point, positioned to block about half the light"

So basically August Toepler took Léon Foucault's knife-edge test and applied it to gas (for shockwave measurements). What I want to know is how in God's name did either of them figure this out in the first place?
posted by Old'n'Busted at 2:04 PM on July 18, 2017 [1 favorite]


We do something similar where I work called Laser Shadowgraphy to visualize air exiting nozzles. We use a laser with a diffuser filter and a regular projector screen. It's pretty neat, but not as sensitive and needs a mostly darkened room. It doesn't need any precise setup though.
posted by ArgentCorvid at 2:26 PM on July 18, 2017 [1 favorite]


how in God's name did either of them figure this out in the first place?

In the mid 19th century the creation of collimated light beams was a big topic for both communication and ranging. In fact, it's the topic of almost half an episode of the original classic Connections TV series, as the limelight and then arc lights were invented for just this purpose. (Rewatched recently, well worth doing.)

Toepler probably noticed first that relatively minor atmospheric effects were disrupting his carefully created collimated beams. Then he found that the beams could reveal hidden information about the atmosphere that was distorting them.
posted by Bringer Tom at 5:07 PM on July 18, 2017


As seen on the front cover of John Martyn's album Solid Air, fact fans.
posted by Buck Alec at 1:02 AM on July 19, 2017 [1 favorite]


Is there a kind of spectrometry for Schlieren photography, so that you could see what gas you were dealing with, or is this strictly a visualization method?
posted by bryon at 1:34 AM on July 19, 2017


This (https://www.youtube.com/watch?v=IZ0bYi9UFv8) is a pretty decent breakdown, IMO, with build tips (including a part list AND sources for said parts)
posted by Samizdata at 1:42 AM on July 19, 2017


Watching this made me wonder if some birds (like some raptors, or vultures) that spend their time finding and soaring in thermals have a way of seeing air currents?
posted by Dip Flash at 4:16 AM on July 19, 2017


Is there a kind of spectrometry for Schlieren photography, so that you could see what gas you were dealing with, or is this strictly a visualization method?

All you could possibly math out is how the density of the gas changes across the field.
posted by aubilenon at 9:39 AM on July 19, 2017 [1 favorite]


This is insanely amazing work from 2011.

Wow, that's incredible.
posted by Copronymus at 8:11 PM on July 19, 2017


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