Why are Railway Signals 'Semaphores'

I have been preparing a talk to a local history society about the role of the Victorian Station Master.

The man who was seen by many as being the epitome of the local manager didn't exist in the early railway. What they did have were Special Constables who were responsible for the regulation of trains on the new fangled railway. This was usually done by little more than lamps and flags. Which when there may have been only 4 or 5 trains a day was quite effective. But over time lamps and flags were no longer able to keep pace with the increasing numbers of trains being run.

So to make the Constables life a little easier we was provided with some simple signals. The picture shows such an installation somewhere on the Brighton line. The basic design of the equipment was taken from the old Naval Semaphore Signal stations that were located on all the high points on a line from London to Portsmouth; that's why there's a Telegraph Hill in Brixton.

Over time the role of the Constable operating the semaphore signals was overtaken by a signalman (just as they were in the Royal Navy) and the Constable morphed into a Station Clerk and then a Station Master.