The persistence of engineering

The ubiquitous cigarette lighter socket

Have you ever read that old ditty about the persistence of engineering? In case you haven't, I'll repeat it here for you:

The U.S. standard railroad gauge (distance between the rails) is 4 feet, 8.5 inches. That is an exceptionally odd number. Why was that gauge used?

Because that's the way they built them in England, and the U.S. railroads were built by English expatriates.

Why did the English build them that way?  Because the first rail lines were built by the same people who built the pre-railroad tramways, and that's the gauge they used.

Why did "they" use that gauge then? Because the people who built the tramways used the same jigs and tools that they used for building wagons, which used that wheel spacing.

So why did the wagons have that particular odd spacing?  Well, if they tried to use any other spacing, the wagon wheels would break on some of the old, long distance roads in England, because that's the spacing of the wheel ruts.

So who built those old rutted roads? The first long distance roads in Europe (and England) were built by Imperial Rome for their legions.

The roads have been used ever since. And the ruts in the roads? The ruts in the roads, which everyone had to match for fear of destroying their wagon wheels, were first formed by Roman war chariots.  Since the chariots were made for (or by) Imperial Rome, they were all alike in the matter of wheel spacing.

The U.S. standard railroad gauge of 4 feet, 8.5 inches derives from the original specification for an Imperial Roman war chariot. Specifications and bureaucracies live forever.  So the next time you are handed a specification and wonder what horse's ass came up with it, you may be exactly right, because the Imperial Roman war chariots were made just wide enough to accommodate the back end of two warhorses. Thus we have the answer to the original question.

Now a twist to the story... When we see a space shuttle sitting on it's launching pad, there are two booster rockets attached to the side of the main fuel tank. These are solid rocket boosters, or SRB's. The SRB's are made by Thiokol at their factory in Utah.

The engineers who designed the SRB's might have preferred to make them a bit fatter, but the SRB's had to be shipped by train from the factory to the launch site. The railroad line from the factory had to run through a tunnel in the mountains. The tunnel is slightly wider than the railroad tracks, and the railroad tracks are about as wide as two horses' behinds.

So, the major design feature of what is arguably the world's most advanced transportation system was determined over two thousand years ago by the width of a horse's ass.

I think you get the parallel. When it became necessary (back in the 60's?) to have a source of 12V in cars for some newly developed accessory, the cigarette lighter socket got pressed into service as the source of that 12V - it was right there, in every car.  Plugs were developed to tap that resource.

Today, cars still all come with that cigarette lighter socket, but no actual cigarette lighter.  And the socket is not labeled 'Cigarette Lighter' - it is simply called '12V', if it has any label at all. 

Modern generations of kids have no idea why a 12V source in a car needs to have such an awkward size and shape, not knowing its origins.  And they are right.  It is only because of 'persistence of engineering' that we are saddled with these things. 

But today a new standard is emerging: the USB plug.  The USB (Universal Serial Bus) standard was developed as a means for data transfer.  The provision of power via the plug was almost an afterthought.  And yet today, every cell phone, eBook, and in fact virtually every electronic device with a rechargeable battery inside it (even my remote control helicopter), uses a version of USB plug, not for data, but for power.

The new standard.  But with a still familiar shape...

To provide USB sockets on a boat, the old molds for the cigarette lighter socket were used to make the outer casing.  And because of that, the new socket will fit in the hole exposed when a cigarette lighter socket is removed.  For new installations however, it remains to be seen whether a more compact form factor will appear in the future. 

You are seeing a real, live case of persistence in engineering, right here in River City.

The persistence of engineering