From:	David Woods <david@*******.FREESERVE.CO.UK>
Subject:	Re: thermographic vision-question
Date:	Wed, 3 Feb 1999 18:48:03 +0000

"D. Ghost" wrote:
>
> On Tue, 2 Feb 1999 20:30:40 -0500 Paul Gettle <RunnerPaul@*****.COM>
> writes:
> >-----BEGIN PGP SIGNED MESSAGE-----
> >At 11:00 PM 2/2/99 +0000, David Woods wrote:
> >>As for Sonar, I can't imagine solid objects being transparent to sound
> >>waves. Although, admittedly it's not my field.
>
> Disclaimer: What follows is what I remember of the physics of sound... :)
>
> Actually, the speed at which sound travels depends on the state of
> matter: Sound travels through Gas the slowest. Faster through Liquid and
> fastest through Solid. In fact the reason sounds sound funny underwater
> is because the sound moves so fast that it messes with your ability to
> tell where it's coming from.

After a little thought I've realised something.

To sound, density would be a lot like refractive index to light. So a
sound wave travelling through air encountering a solid would tend to be
strongly reflected.

> >You've obviously _NEVER_ lived in a college dorm then. :)

I was the one making the noise. (I wish)

Regards

- David Woods