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Re: white



Sorry about the incorrect subject title in the previous post.

See Bohren's excellent discussion of necessary vs sufficient conditions on
page 107 of Clouds in a Glass of Beer for the answer.

The particles are sufficiently large to scatter visible light equally. But
there are a sufficient number and concentration of particles that multiple
scattering would result in a white cloud even if they weren't large.

A few drops of milk in water scatters blue light preferentially. But many
drops result in multiple scattering and white milk - even for the milk
particles smaller than the wavelength of light.

Larry Woolf;General Atomics;San Diego CA
92121;Ph:858-526-8575;FAX:858-526-8568; www.ga.com; www.sci-ed-ga.org

-----Original Message-----
From: Robert Cohen
Sent: Friday, April 11, 2003 2:06 PM
Subject: Re: white

Larry Woolf responds to the "what makes clouds white?"
request with subject line "Re: hoaxes".
Rather than repeat what has already been written,
I suggest the following thought experiment.

The question is whether...

#1: Do small cloud drops preferentially scatter shorter
wavelengths and large cloud drops preferentially
scatter long wavelengths?

=2E..or...

#2: Are all cloud drops so large as to scatter both short
and long wavelengths equally well?

Both would produce white light. However, theory #1
predicts that clouds with uniform cloud droplet size
(if they exist; a common charge of those who explain
corona phenomena) would be a specific color while
theory #2 predicts those clouds would still be white.