Re: ATM BVC Weirdness part II

[mjc5 <mjc5@psu.edu>]

Aplanatic@aol.com wrote:

> As you might recall, the thermal diffusion time constant goes like the length scale squared.  Thus, it thermalizes quickly through its thickness but very, very slowly across its diameter.  A two inch thick Pyrex mirror has a thermal time constant of about 15 minutes in the thickness direction, but a time constant of many hours across its diameter.

	How exactly does this work? I've been sitting here, scratching me head,
and can't get it. How can a mirror have two different thermal time
constants? Is this to say that the expansion and contraction has a
significant time lag after thermal equialization, that is to say that
the mirror is at ambient temp, yet still at a non equalibrium state of
expansion?

	- Mike -