signals -- Mr Cochran's Question re Marker Lamps on N&W Semaphore Signal Masts

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Cardinal von Cochran, Excellency:

Much could be said about this matter. I will try to be brief, and answer by giving only the necessary elements of the history.

Signals using oil lamps for illumination were subject to the source of illumination (the fravile oil flame) being obscured or extinguished. The flame might be blown out by the wind, the oil pot may run out of fuel, the roundel (lens) may be plastered over by snow, etc.

Such conditions presented a safety problem at any signal, but the situation was especially critical at a Home Signal. (A Home Signal is a signal which governs movement over the routes of an interlocking.)

To help mitigate the risks of a "dark signal" at an interlocking, sometime around 1900 the largest railroad in the country began installing an additional oil lamp (displaying red) below the operating arms of a semaphore signal. These were called "marker lights." This was not an infallible remedy, but it was a step in the right direction. If the lamp(s) behind the semaphore roundels went dark, there was at least a red light for the crew to see and keep from running past the signal. The PRR went so far as to use TWO red lamps (side by side) at the bottom of a signal governing entrance into a Manual Block.

The N&W also used a "marker lamp" on the mast, below the arms of semaphore signals, at least in places. Right up until the last PL signals were retired from the Bristol Line, you could still see the blanked-out "hubs" where "marker lamps" had been mounted low on the signal masts. (The N&W "marker lamps" on PL Signals were just plain cast iron box-like lamp housings used on all PL signals, and they displayed that amber color known in the industry as NOVIOL.)

Now, transition to the era of electric lamps used in signals, which began around 1910. The signal people were still in fear of the dangers of the "dark signal." The inventor of the Position Light Signal, Alexander Holly Rudd, arranged his lamps three-in-a-row so that signal aspects could be distinguished even if a lamp burned out.

When the N&W got into the Position Light Signal business (early 1920s,) for a brief time they continued the practice of adding as "marker light" below the arms ("heads," as some people say) of the PL signals.

There is one Union Switch & Signal Co. photograph which shows a very interesting N&W signal at Home Creek on the Pocahontas Division, where a Home Signal is equipped with three full Position Light arms, plus a "marker light" below them. I will attach that photograph. My guess is that the top arm conveys the condition of the first automatic block behyond the interlocking; that the second arm conveys the speed through the routes of the interlocking (high speed or medium speed route, as the logic of old signaling called them;) and that the bottom arm is the "Calling On" signal, equivalent to today's Restricting aspect, used when due to some abnormal condition (broken rail, switch not locked up, etc) a favorable signal could not be given through the interlocking. And then, below it all, is that old-timey "marker light." So, "marker lights" were used on both Semaphore and PL Signals (at least in some locations,) Red in Semaphore days, "NOVIOL" yellow in N&W Position Light Signal days.

There is one more element of your question which I am unprepared to answer, namely the thought process by which the early "marker lamps" transitioned into the "Stop and Stay" lamp used on some later N&W PL Signals. Sorry, but I have just not thought through the historical steps of that issue.

This should answer most of your questions. But if you want more, come back when you get some more money and we will discuss some other solutions to the "dark signal" problem, e.g. double filament signal lamps ("bulbs," in the vocabulary of some folks) and the use of Light Out Relays. And I will attach a couple photos of those very clever devices, too.

If you want my collection of articles on the development of the Position Light Signal, go here... and do send in a generous donation to the Retired Old Brakemen's Fund !

https://drive.google.com/drive/folders/1PgtjCL7I7bNKFxAd7zvt_oJ-PPNfyWT1?usp=sharing

https://drive.google.com/drive/folders/1ek6SP4jXRDo5vnKJYZtdWWhuQ4tGxLBK?usp=drive_link

Cheers from the Kingdom of White-and-Slippery, the Shoveler's Delight.

-- abram burnett
Magnetohydrodynamic Combined Cycle Fuel Cell Turnips, ver. 2.0
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