NavList:

Good Morning and thanks for the input, David.

The movement in my water tray isn't the  kind of shimmering that I once did see when I used just a deep open tray without any covering.

Presently, the water surface  appears to swirl very slowly up and down the length of the tray, the effect is mesmerising, somewhat like the motion of those, 'God's Hankies" made by oil stains atop of sluggish water.

Practically and certainly most noticable at Local Apparant Noon, I see a sight image which slowwwwly floats the limb to limb contact in and out, over an amplitude of around 2 mins of arc...and I try to chase this measure with the micrometer.. the images would appear to be moving independantly...surely not?.  There is only around a 5 mm depth of water in a 15x10x1.5 cm tray.. a tray made for the hospitality trades, for tipping gratuities, and comes with no apparant magical properties.

There's something I forgot to include in post 1 and it is that I have been much aware that the water surface is clinging to the inner edges of the plastic tray and has crossed my mind that perhaps this attraction is causing a meniscus effect on the water surface, one which, presumably, counters the effect of gravity wanting to flatten the surface. 

Anyway, I am happy that  I am not the only one to have the impression that the huge thermal mass of buildings can have the potential to mess up the best of hallowed Refraction formulae.

Loz Elms