Wednesday, May 4, 2016

Before there was the Internet, there was....Semaphore!

Boy Scouting and I didn't really get along too well. I hated camping, and I thought nature was best viewed from the comfort of a hotel room. None of this was helped by the fact that my Boy Scout Troop was the most amazing collection of losers and goofballs ever assembled under the Boy Scout umbrella. At our local camping competitions, we would invariably finish last. Our scoutmaster became so enraged at one of our meetings that he threatened to walk out and never come back if we didn't settle down. We took this as the usual empty adult threat (did your dad ever really turn the car around and drive back home on the way to a family vacation?) So we kept up our antics. Much to our surprise, our scoutmaster did walk out of our meeting, got into his car, and drove away, never to be seen again. Thus ended my career in Scouting.

But I did learn a few worthwhile things in the Boy Scouts. I can tell the difference between venous bleeding and arterial bleeding (the difference is that arterial bleeding means you're going to die). I can identify poison ivy -- most of the time, anyway. And best of all, I learned semaphore.

Semaphore was an early version of the internet. Packets of information, called "letters" were encoded as positions of two signal flags and transmitted through the air over literally tens of yards. Transmission rates of 1-2 bytes per second were possible.  (Quiz: with two signal flags, and eight different flag positions, how many different letters can be encoded? The two flags cannot occupy the same position).

Semaphore plays a role in L. Sprague de Camp's classic novel, Lest Darkness Fall. The protagonist finds himself hurled back in time to the last days of the Roman Empire, and he sets about trying to stave off its collapse. It's an interesting idea -- what are the "doable" technological improvements you could introduce to the ancient world? He starts with Arabic numerals and eventually introduces a system of cross-country semaphores to allow for rapid communication across the empire. But this raises an interesting question -- why didn't ancient civilizations, or for that matter, any pre-telegraph civilizations, use systems of semaphore towers?

I have no idea, but if I had to venture a guess, it would be that a system like this would not be competitive with a messenger on a fast horse. And of course a semaphore chain would be susceptible to errors creeping in at each relay point. There are no "error-correcting codes" for semaphore.

To answer the question I raised earlier, 8 different positions for two semaphore flags gives you (8x7)/2 = 28 different possible letters, a rather convenient number! This wouldn't work for Russian, which has 33 letters in its Cyrillic alphabet. No wonder we won the Cold War.


Joe said...

Semaphore towers were used! For a glorious run of about 50 years before the telegraph was invented. See here They were much faster than messengers in some cases.

In fact, the boy scout version of semaphore is based on these towers. Napoleon's greatest accomplishment.

Kathy said...

Ah, but Martin Padway introduced the telescope along with the semaphore. Absent a means to see farther, the towers would need to be set too close together to be economical.

BTW, I love de Camp's story.