In your periscope, light hits the top mirror at a 45-degree angle and reflects away at the same angle, which bounces it down to the bottom mirror.
(light; hits; the top mirror; T:at a 45-degree angle; L:In your periscope) (light; reflects; away; at the same angle; L:In your periscope) (the same angle; bounces down; it)
light light the same angle
hits reflects bounces down
the top mirror T:at a 45-degree angle L:In your periscope
away at the same angle L:In your periscope
it