I just googled it.
Apparently Newton proposed that the attractive forces within different mediums interfere with the net force of attraction. For instance, since water exerts a greater attractive force on the particle of light it causes the light to experience a greater velocity downwards, towards the gravitational pull. Likewise, light coming out of water into air gains a greater attraction due to gravity as opposed to air particles causing the light particle to bend closer to the water.
With respect to reflection, it's simply a matter of individual particles bounding off of surfaces forming images (and particles without enough energy to penetrate transparent surfaces are the sources of reflections on those surfaces).
