Mac, Unless my memories of school physics desert me, whilst a ray of light is bent towards the normal on entering the glass (because of the change in refractive index), it is then bent back by exactly the same amount as it exits the glass. All that your three panes will do is to shift the ray sideways, but it will still be parallel to the ray incident on the outside of your window.
If your three panes are actually triple glazing, there may be vacuums between the sheets which would mean that the ray in the gaps would not be parallel to the incident ray (because the refractive index of a vacuum is not quite the same as that for air). The ray would be bent back more (I think) as it emerges into the vacuum between the first two panes than it would if it were going into air. Having a vacuum both sides of the middle pane, the ray out of the middle pane will be parallel to the one going into it (though neither will be parallel to the ray incident on the outside of the window). Finally, the vacuum/pane/air combination of the last sheet will reverse the change of angle effects of the first air/pane/vacuum combination! Ultimately, when it emerges back into the air, the exiting ray will be parallel to the incident ray once again. If you want to convince yourself further, I think the correct formula is (sin i / sin r) = refractive index where i is the angle between the incident ray and a line perpendicular to the surface, and r is the angle between the bent ray and the same perpendicular. Hope this helps! David Higgon London
