We all know that the earth is a sphere.

The book Longitude by Dava Sobel tells the story of John Harrison who figured out how to calculate how far east or west a ship was on the ocean.  A few weeks ago I talked about the ship’s log.

Once sailors knew how to calculate longitude accurately they no longer had to throw chunks of wood over the side to calculate how fast they were going.  Figuring out how far north or south you were had been known since ancient times.  As long as the night was clear you could measure the distance from certain known stars to the northern or southern horizon and get an accurate fix on your latitude.

But since the earth spins always eastward that trick doesn’t work with longitude.

Instead, Harrison developed a highly accurate clock that could survive the motion, salt, humidity and temperature variations of an ocean voyage so that a navigator could check when noon occurred at his location and compare it to the time back in England.  Six hours difference for instance would mean he was a quarter of the way around the world.

So what does all this have to do with etymology?

Longitude is from Latin and it means what it sounds like, a measurement of length.

Latitude is also from Latin and is related to “lateral” that is from side to side and refers to the width.  The implication here is that the world is longer than it is wide; which isn’t true if the world is a sphere.

Brewer’s Dictionary of Phrase and Fable tells us that the ancients didn’t have a full grip on the world and figured the Atlantic stretched to the west while terra firma stretched to the east, in both cases further than one could fathom. This was the long dimension.

The width of the world began somewhere south of the Mediterranean and ran northward.  The scope of this was a better understood.  And so our words adopted from our ancestors carry with them this seemingly inaccurate sense.

But here’s the rub:  Longitude is measured around the whole equator while latitude is measured only from pole to pole—the degree of northness or southness is the same on either side of the globe—so there is in fact half as much latitude as longitude.

What’s more, because the world spins, it bulges a bit at the equator, so it is a little bit longer around the middle than around the poles.