On Tue, 28 Oct 2008 21:40:57 -0000, "John"
wrote:

I just wondered why Yale locks were always fitted at eye level but mortise
locks were fitted half way up the door (traditionally)

A mortice is a real lock designed to prevent people breaking in and
goes in the strongest part of the door.

The Yale is termed a "night latch" by the yanks and that just about
sums it up.