The Factor Factor
Although I'm not an expert in the art of navigation, I rarely get lost on the way to work (two GPS receivers in the car) and I do find the subject interesting. Long ago, both for reasons of curiosity and profession, I joined a specialist organization that concerns itself with the arcana of finding one's way around on the surface of the earth and nearby space. Their journal can be counted on to liven up a rainy day with discussions of Lense-Thirring precession and other relativistic corrections to GPS data. An additional pleasure of membership is exposure Joe Portney's Ponderables" which are "navigation puzzles, controversies, historical problems, and other ponderables demystified by an expert navigator..."
In one column he introduced me to the Pulfrich effect, with, I felt, an incorrect explanation. Needless to say, I was compelled to whine about this with the following conservation-of-text result. Nobody has offered me an effect in my own name yet, but I won't rest until I have one...
NAVWORLD QUARTERLY NEWSLETTER
|Portney: A reader of “3D with Half a Pair” from my book Portney’s Ponderables provided me with this correction:|
|I just read your explanation in the ION newsletter and it left me
puzzled. You keep referring to the “delayed” light path and in one case
mention an “out of phase condition.” This seems highly improbable to me.
While it is true that electromagnetic radiation is slowed by a
dielectric such as a piece of glass, the delay in a case like this would
be picoseconds at most, far too short for any physiological recognition
of time differential. Rather I think what is happening is that, due to
attenuation rather than the delay , the eye’s response to the light is
slowed, and that causes the effect.
Actual time delay plays an important part in hearing localization. Light is more than 5 orders of magnitude faster than sound, and the eyes are closer together than the ears, so I think it’s attenuation rather than delay! Given that correction, it’s an interesting piece. I ‘d never heard of the “Pulfrich Effect” and I’m glad to learn about a new one.
It must be nice having one’s own “effect.” I’d settle for a less resplendent “Factor factor.”
|To which Mr. Portney replied:|
|Factor is in general correct. The delay occurs in the brain as the brain tries to merge the images received from each retina but owing to the attenuation of the image received from the covered eye the merging of the signals in the brain experiences a slight delay (there is an out of phase condition) and this is the cause of the 3D effect. It is interesting to note that Pulfrich was blind in one eye and was never able to view the effect that he discovered. But just as Beethoven was able to compose even as he grew deaf , Pulfrich was able to envision the 3D effect mentally without empirical verification.|
Today's educational blog was sponsored by the USDUC. Who says they don't perform valuable work?