Hello All, Tony wrote:
>> I can't speak for other areas but hereabouts the interglazing space in double glazing is filled with argon, not air, from which it has a different 'refractive index' - I think my physics teacher might have said if I'd had one. (WW2 - no teachers - just nuns!) Does the maintained parallelism of an air/glass/air/glass/air interface still apply? << Yep! It sure does! Chuck [EMAIL PROTECTED] PS: Patrick - Thanks for the pointer to Sellotape. I'll check it out. Edward - Thanks for the pointer to Edmunds Scientific. I had forgotten about them.