Fwd: signal apparatus

[NW Mailing List]

So, for the benefit of silhouetting, the excessive height would have 
been pointless in the hollows of the Pocahontas Division (?). Nice.

The arms for each route were "ranked" by route speed from high to low 
and that relative height was maintained across adjacent masts on the 
same bridge or, particularly, bracket signal. Thus, the height is 
staggered between masts and otherwise similar arm arrangements of 
bracket signals at the ends of sidings.

Thanks, Abram. How's that book coming along?

Grant Carpenter,

bloviating weenie
and aspiring curmudgeon

On 1/28/2016 10:15 PM, NW Mailing List wrote:
> The "boxes" you inquire about on the signal cantilever are old semaphore cases. They originally housed the motor and sprocket-and-chain drive apparatus for operating old Style S and Style B semaphores, along with the track relays and relays for line circuits.
>
> You have seen many, many of these on the old N&W, but they were on the ground, not on a signal bridge.
>
> When N&W installed PL signals, they used simply removed the semaphores arms and motors, and mounted the new PL's on the old masts and cases.
>
> One reason the masts for N&W PL signals were so high is that they originally were built for the spacing of two and sometimes three semaphore arms, which required more room than PL signals.
>
> Two semaphore arms (again, don't say "heads"... that's a weenie word) were required to give the indications which could be displayed on one PL arm. And THREE semaphore arms were required to give the indications that could be displayed on two PL arms. So, it was necessary that semaphore masts be higher.
>
> There is also another reason for the height of the old semaphore masts, and although it goes beyond the scope of your question, I will explain it. In semaphore days, there was a notion that the ideal way to locate a semaphore was so that, when sighted by the Engineman, the signal arms were viewed against the sky. It was felt that if trees, mountains and the like, formed the background, they "competed" with the visibility of the semaphore arms. This was the fundamental reason for the very high masts, and it was good thinking. One additional benefit of such an arrangement was that it raised the signals up above the pall of smoke which often hung over heavily trafficked, double track main lines. But apparently not all railroads subscribed to this notion. For example, the Santa Fe had remarkably low semaphores, whether they be bridge signals or ground mast signals.
>
> Allow me one further ramble... If you compare the 1938 N&W Rule Book (the rule book which first depicted PL signals) with the 1928 Rule Book (which depicted only semaphores,) you will discover a very interesting thing. To wit, that when the N&W first installed PL's, they used them for NOTHING MORE than replicating, with rows of lights, the positions of the old semaphore arms. That is to say, if the old semaphore had three arms, the N&W replaced it with a three arm PL. Now that is truly amazing, especially since someone had worked out, in 1922, a system of giving a full set of signal indications with only TWO PL arms. (His name was Alexander Holley Rudd, and he was the Chief Signal Engineer for another railroad.)
>
> To exacerbate this, below the three full PL signal arms, the N&W sometimes used a "marker light" at the bottom. Technically, that constitutes a "four arm" signal. It's function was to show that the signal was not an automatic, and that its most restrictive indication was Stop, not Stop and Proceed. When these marker lights were removed from the masts, the hubs were left on the masts and a blanking plate was placed over the opening in the hub. Those old hubs, which formerly held the marker lamps, can still be seen on many N&W PL signals.
>
> If you look at the 1945 N&W Rule Book, you will see the same three arm PL's shown that were shown in the 1938 Rule Book.
>
> If you check the 1951 N&W Rule Book, however, the old three PL arm signals are gone. Someone in the N&W Signal Department had learned about the PL signal arrangements created by Alexander Holley Rudd in 1922, the old third arms had been removed, along with the bottom marker lamps, and a full set of indications was now being given with just two PL arms. The new, more simple arrangement saved relays, a lot of wire, lamps and electricity.
>
> By the way, when referring to the arms on a signal, they may be referenced two ways. The standard plans and engineering prints designate them as the A, B and C arms. But in conversation, they are usually called the top, middle and bottom arms.
>
> You asked me for the time, and I told you how to build a clock. But sometimes too much information is better than too little.
>
> And some day, if you want to know about FIVE arm signals, we can have another interesting discussion!  But that one will involve some very, very deep history.
>
> -- abram burnett,
> a simple turnip farmer
>
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