Re: [ATM] Temperature-changes

[Ross Sackett <rsackett00@yahoo.com>]

--- Mark Holm <mdholm@telerama.com> wrote:

>...  The layers of the mirror
> closer to the 
> surface heat or cool more rapidly than the inner
> portions.  This causes 
> the warmer or colder portions of the mirror to
> expand or contract with 
> respect to the rest.  Since the glass is not
> expanding and contracting 
> uniformly, stresses are set up that deform the
> mirror shape slightly. 

Mark,

Since the edges of the mirror are thicker than the
center, all else equal I'd think they would
equilibrate with the air more slowly.  As the evening
cools, the delayed shrinkage of the edges would lead
to a degree of overcorrection.  Most of us in trying
to speed things along have been blasting the center of
the mirror with a back fan.  Seems to me that would
temporarily make the situation worse and lead to
greater overcorrection.  Would it make more sense to
ventillate the edges rather than the center?

Ross 

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