When signals were introduced

In the next issue of Underground News there will be a piece about the end of 'S' prefixed Automatic signals, along with a few other notes. It doesn't answer the original question though.

What did the S denote?

Oh! Fair enough, nice and simple, thanks On the basis of railtechnicians comment - was it used with Automatic signals only, or all signals?

All Underground lines had 'S' automatic signals in the early years, including the Met.

Electro-mechanical signalling was later, it was certainly not the case in the early days. Let me explain why, but first I will have to put this into context...

Up until the opening of the C&SLR, there had only been some electric locomotive and tramcar experiments. There were no other electric railways and there was very little electricity anywhere. In fact the power station that the company built at Stockwell was probably the biggest in the world at the time of its opening - and it was small. In fact, there was not quite enough electricity to operate the railway efficiently (they quickly added more power) and certainly not enough to light the stations (they used gas).

Across other railway companies, electricity was virtually unheard of. Signals everywhere in the world were illuminated by oil or gas, with some stations and trains supplementing this type of lighting with candles.

When signals are illuminated by a flame, it is not feasible for a signalman to extinguish and reignite different coloured signals lights from a distance. It is far easier to move a coloured glass that can be moved in front of a flame. That why there is a spectacle plate on the end of mechanical signal arms and that it is how all illuminated signals worked at the time that the C&SLR was opened for traffic.

When the C&SLR needed a coloured light signalling in its tunnels, it was either a case of using existing technology or trying to find a way of controlling a primitive electrical circuit from a mechanical signal frame of the type that was needed to control the interlocking. We can easily discuss alternatives with the benefit of both hindsight and subsequent developments, but this was unexplored territory in 1890 and the company do not seem to have had the time, the inclination or the money to try to develop a new system that may or may not have worked. It was far easier to stick as closely as possible to an off-the-shelf approved system.

Thus the tunnel signals were adapted so that they were illuminated by a fixed electric light instead of a fixed oil light, but with redesigned spectacle plates so that they occupied a minimum amount of space. Other than that, the cable that controlled them only needed to be slipped inside some gas piping to get it round the curves in the tunnels. Result - pretty much a conventional mechanical system.

It's neither needless nor abrasive, it's a statement of fact and it was not addressed to you!

All too often people in this place answer questions that were not asked, it is easily done when quickly scanning threads trying to sort the wheat from the chaff. That is not to suggest that the irrelevant reply to my question was uninformative to others, indeed I made no such suggestion.

On the other hand your comment is unnecessary and designed to be offensive, which it is, I'll take no lessons in political correctness from you or anyone else whether you begin your unwarranted words of lecture with 'please' or not. If you don't understand written English then have enough respect to hold any intended comment until you do!