If two mirrors are used the light ray is made to change direction twice.
In this picture the torch is at the left hand side. The slit is near the middle of the picture and the single ray of light can be seen traveling right where it reflects from the mirror and travels downwards to the second mirror. It changes direction again when it strikes the second mirror and travels to the right again.
This double reflection is made use of in a very simple but important invention called the periscope.
This picture shows a periscope in use in the trenches in the Great War of 1914 to 1918.
The soldier looks into a mirror in the bottom of the long narrow box and sees the light coming from over the top of the trench wall. There is a mirror in the top of the box collecting light from the battlefield and reflecting it down to the mirror in the bottom.
It allows the soldier to see what is happening on the battlefield without having to put his head up over the trench wall where the enemy might be able to shoot him!