The US standard railroad gauge (distance between the rails) is 4 feet 8.5 inches. That's an exceedingly odd number. Why was that gauge used? Because that's the way they built them in England, and English expatriates built the US railroads.
Why did the English build them like that? 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.
Okay! Why did the wagons have that particular odd wheel 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 was the spacing of the wheel ruts.
So why were the ruts spaced so? Imperial Rome for their legions built the first long distance roads in Europe (and England). The roads have been used ever since. And the ruts? Roman war chariots first made the initial ruts, which everyone else had to match for fear of destroying their wagon wheels and wagons. Since the chariots were made by Imperial Rome, they were all alike in the matter of wheel spacing. Thus, we have the answer to the original question. The United States 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 which horse's ass came up with it, you may be exactly right. Why? Because the Imperial Roman war chariots were made just wide enough to accommodate the asses of two war-horses.
And now, a final twist... There's an interesting extension to the story about railroad gauges and horses' asses. When we see a Space Shuttle sitting on its launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs. Thiokol makes the SRBs at their factory at Utah. The engineers who designed the SRBs might have preferred to make them a bit fatter, but the SRBs 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 SRBs had to fit through that tunnel. The tunnel is slightly wider than the railroad track, and the railroad track is about as wide as two horse's behinds. So, a major design feature of what is arguably the world's most advanced transportation system was determined by the width of a horse's ass!
This might rightfully be in the "rants" section but what the hey?
The way technical matters are 'reported' by the general press is an ongoing pet peeve of mine (OK, yes, I have a lot of 'em). Except for those publications that employ specialized science reporters, the demonstrated level of understanding in stories having tech content typically ranges from poor to abysmal. Give 'em a big number or a seemingly dramatic statistic and they are happy; it doesn't have to make sense or be in any way meaningful in the context of the story.
A simple but universal example is any story involving electrical power, a subject always prominent during the hot summer months when power use peaks. My peeve? The nonsensical reporting of power figures.
Electrical power can be (and frequently is) usefully compared with water, but the comparison can invite confusion, as we will see.
As a water consumer, you are most interested in two items: Is there sufficient water flowing out of the tap when I turn it on, and: How much water am I using and will have to pay for? Water flow rate is measured in gallons-per-minute (GPM) and water quantity is measured in gallons (although your bill probably shows quantity in a mysterious measure called 'units', each normally representing 748 gallons).
The same holds for electric supply. For electric power, the corresponding measures are in watts, or more conveniently, kilowatts (1,000 watts). Kilowatts (or KW), by themselves, are a measure of flow rate, as gallons-per-minute are for water. Instead of gallons, the quantity of electric power is expressed in kilowatt-hours (KWH), which translates to one kilowatt flowing for one hour. Notice that the comparison with water becomes misleading; one gallon represents an actual quantity whereas one kilowatt represents only a rate of flow.
Most reporters get no farther than kilowatts, or for bigger numbers, megawatts (1,000,000 watts). Hundreds of times I have seen statements like "the new wind farm generates XXX kilowatts, enough for XXX homes". The reporter thinks this statement makes sense, but it really doesn't mean anything at all. To make it somewhat meaningful they would have to say "in an average month the wind farm is expected to generate XXX kilowatt-hours, the amount used by XXX average homes". Unfortunately these meaningful numbers will not be nearly as satisfying to wind-power advocates or the wind-farm salesmen, so the reporter, not knowing what questions to ask, will simply parrot the meaningless numbers these individuals feed them. (For a small expansion on this topic, see my letter to a local paper)
I will admit that, in California at least, they sometimes properly quote peak flow rates, as in "today's power consumption reached a peak of XXXX megawatts." Too often, however, they translate this back into the meaningless "today California used XXXX megawatts". At least you can usually guess what they are trying to say.
Another area where comparison with water can be misleading is that water can easily be stored up behind dams for use on demand later on. Not so electricity, a fact that many reporters & writers cannot comprehend. There is simply no efficient way to 'store up' large amounts of electricity to meet a later peak demand (yes, you can pump water uphill, compress air into underground caverns, heat salt deposits, etc, but these are all subject to large losses). You must have enough functioning power plant capacity to supply the maximum demand on a blistering hot summer afternoon. This means that all those stories you see saying things like "adding this wind farm will replace XX number of nasty power plants" are totally false. Wind (and solar) are fickle energy sources. Sometimes you have wind, or sun, and sometimes you don't. The power companies must still build and maintain enough gas / coal / hydro / nuclear generating capacity to provide 100% of the maximum demand, otherwise someone will have to do without power just when they want it most. Don't get me wrong, wind and solar ARE good for reducing the overall fuel consumption of the gas or coal plants, which certainly may be justification enough. But it is the height of foolishness to say they can take the place of conventional power plants.