How did humans send warnings?

Join Mira and Finn on History's Not Boring by Kidopoly as we race against the clock to answer a life-saving question: before text messages and electricity, how did humans warn each other of danger? Imagine seeing enemies approaching and having to send a warning as fast as possible! Thousands of years ago, ancient civilizations lit massive signal fires on hilltops. Did you know the Great Wall of China had special beacon towers that could pass a warning message 700 miles in a single day?! Wow! We'll travel back in time to hear medieval village church bells ringing out in panic, and meet Claude Chappe, a French engineer who built giant moving wooden arms to wave messages across the country! Discover the invention of roaring ship sirens and learn how loud air raid sirens protected London during the Blitz. Finally, we'll blast into the present day to explore high-tech ocean tsunami buoys and earthquake alarms that give people a precious 30 seconds to get to safety! Get ready for a loud, exciting, and action-packed adventure through time!

Transcript

SPEAKER_00 0:00

Welcome to History's Not Boring by Kidopoly.com. I'm Mira. And I'm Finn. Today we want to give a massive shout-out to Graeme Lovelace, tuning in from West Richland, Washington.

SPEAKER_01 0:12

Hey Graham, thanks for listening.

SPEAKER_00 0:14

Graham told us his absolute favourite episode is the Rockets one. Well, today we're exploring another incredible way humans have used technology in science, looking at the fascinating history of warning systems.

SPEAKER_01 0:29

That is such a cool topic. Like, how did people know danger was coming before cell phones and emergency alerts?

SPEAKER_00 0:36

Exactly! It's one of the most original topics we've ever covered. And to start us off, I have a mind-blowing fact for you. Hit me with it! Today, Japan has an earthquake warning network so incredibly fast, it can give millions of people up to 30 precious seconds to hide before the ground even starts shaking.

SPEAKER_01 0:58

Wait, 30 seconds before the earthquake actually hits? How do they predict it?

SPEAKER_00 1:04

They don't predict it. The system is just faster than the earthquake itself. It's a technological marvel.

SPEAKER_01 1:11

But 30 seconds doesn't sound like a lot of time to get ready.

SPEAKER_00 1:15

It might not sound like much, but when a building is about to shake, 30 seconds is enough to save your life in. But thousands of years ago, getting even a five-second warning was nearly impossible. So how did they do it? Well, before electricity, human beings could only send a warning as fast as a horse could run or a ship could save.

SPEAKER_01 1:38

Which is what, maybe 30 miles an hour for a really fast horse?

SPEAKER_00 1:43

Exactly. If an enemy army was attacking, you had to physically send a messenger galloping across the country. But then, ancient civilizations figured out something brilliant. Light is way faster than horses. Oh, like signal fires! Yes! The most amazing example is the Great Wall of China, which stretches for over 13,000 miles. How did they use it for warnings? They built elevated platform structures along the wall's defensive perimeter. If guards saw invaders, they'd light a fire at night or use smoke signals during the day. Wait, just normal smoke? Wouldn't that blow away? Actually, they often burned dried wolf dung.

unknown 2:28

Haha!

SPEAKER_00 2:28

Wolf poop? Ew! Why would they burn that? Because it made super thick, dark smoke that shot straight up into the sky and was easy to see from miles away. The soldiers actually called them wolf smoke towers. That is disgusting but brilliant. How fast could the warning travel? By passing the signal from tower to tower, soldiers hundreds of miles away could receive the warning immediately.

SPEAKER_01 2:55

Hundreds of miles! A horse could never do that.

SPEAKER_00 2:58

Never. It was like an ancient telegraph system made of fire and poop. Right. In medieval Europe, they used sound instead. If a village was in danger, they would ring the giant bronze church bells. Like, just ring them as loud as possible. Yep, clanging them in a panic. But fast forward to the 1790s in France, a French engineer named Claude Chap wanted to send actual words over long distances. Did he use bells for that? Nope, he built an incredible system of giant wooden towers with massive moving arms on top, called a semaphore telegraph.

SPEAKER_01 3:36

Wait, like a giant wooden robot waving its arms.

SPEAKER_00 3:41

Kind of. Each arm could assume different angular positions, making 49 combinations. Each position meant a different letter or symbol.

SPEAKER_01 3:51

So a guy in one tower looks through a telescope, sees the arms, and then copies the exact same pose on his tower.

SPEAKER_00 3:58

Exactly! They built a massive network, and in 1794 they sent a message from Paris to Lille, which was about 143 miles away. How fast could the giant arm send a message? The message passed through 15 stations and took just nine minutes. That's incredible! It was! Before Claude Schapp, a message on horseback would take two whole days to cover that distance. But visual signals are no good if there's thick fog or it's pitch black outside. In 1799, a Scottish physicist named John Roberson invented something completely new while working on organ pipes.

SPEAKER_01 4:41

Wait, like a musical instrument?

SPEAKER_00 4:43

Yes, he created a pneumatic tube with a spinning wheel that made a continuous loud tone. But it was just used for music at first. Did someone make it louder? They did. In 1819, a French scientist named Charles Cagniard de la Tour improved it, and he gave it a very famous name. Was it the siren? Spot on! He called it a siren because his invention could produce sound underwater, just like the sirens from Greek mythology. So they put them on ships for foggy days so they wouldn't crash. Yes, and eventually on police cars and fire engines. But sirens became truly terrifying during World War II. That was in the 1940s, right? Yes. Starting on September 7, 1940, a day known as Black Saturday, the City of London was bombed by enemy planes for 57 straight nights in an event called the Blitz.

SPEAKER_01 5:45

That's so sad. How did the people know when to run and hide?

SPEAKER_00 5:49

Giant air raid sirens would wail across the entire city. When people heard that terrifying rise and fall sound, they knew they had just minutes to grab their gas masks and run. Where did they run to? Was there a safe place? About 177,000 people would shelter deep underground in the London tube stations. Others hid in tiny metal Anderson shelters buried in their back gardens. Those wailing sirens saved thousands of civilian lives.

SPEAKER_01 6:23

So from wolf poop on the Great Wall to giant wooden arms to wailing sirens, what do we use now? How do we get that 30-second earthquake warning?

SPEAKER_00 6:33

Today, our warnings travel at the speed of light, using computers. It relies on highly sensitive seismometers planted all over Japan. How does it outrun an earthquake? When an earthquake happens underground, it sends out two types of waves. First come the P waves. They travel super fast but are mostly harmless. Then come the S waves, which travel slower but cause all the massive destruction. Oh, so the computers feel the fast P waves first. Exactly! The sensors detect the fast P waves and instantly send alerts before the slow, destructive S waves arrive. That is genius! You get a message saying earthquake before you even feel the ground move. Yes! And out in the middle of the ocean, we have something called Dart Boys, which stands for Deep Ocean Assessment and Reporting of Tsunamis. Do they just float on the top of the water? The buoy floats on top, but it's connected to a pressure sensor, anchored to the sea floor. It measures the water pressure, which changes if a tsunami passes over.

SPEAKER_01 7:42

Wait, how does measuring water weight warn us about a tsunami?

SPEAKER_00 7:46

Because a tsunami moves the entire ocean column from the sea floor to the surface. If a massive wave passes, the pressure changes, and the boy instantly beams a warning to a satellite.

SPEAKER_01 7:59

Wow! Warning systems have gotten so incredibly smart.

SPEAKER_00 8:03

They really have. From passing a message with fire on the Great Wall to instant satellite alerts, giving us precious extra seconds to survive. Humans will always find a way to look out for each other. Alright, Finn, it's quiz time! Let's see what you remember from today's incredible history of warnings.

SPEAKER_01 8:22

Okay, I'm ready. Hit me with the questions.

SPEAKER_00 8:26

First question. What did ancient soldiers burn on the Great Wall of China to make thick black smoke? Next one. Who is the French engineer that invented the semaphore tower network in the 1790s? Question 3. What were the underground train stations in London called where thousands of people hid during the Blitz? Here's number four. What does a dart boy measure at the bottom of the ocean to detect a tsunami? Last question. What are the fast-moving earthquake waves called that give Japan's system the 30 seconds it needs to send a warning? Great job! Let's see how you did. The first answer is they burned dried wolf dung. For question two, it was the French engineer Claude Chapet. Number three, the answer is, they were called the tube stations, or the London Underground. Question 4. A Dart Boy measures the water pressure or the weight of the water above it. And the final answer is, they are called P waves.

SPEAKER_01 9:46

I don't think I will ever forget that they used wolf poop for smoke signals. That is the grossest, coolest fact ever.

SPEAKER_00 9:55

Right? Next time your phone buzzes with an emergency alert, just be very glad it's not a smoke signal.

SPEAKER_01 10:02

Yeah, and we really hope Graham in West Richland, Washington, enjoyed this episode. It was an awesome request.

SPEAKER_00 10:09

We definitely do. Hey, if you love learning cool stuff like this, you should head over to our site, kidopoly.com. We've got tons of fun learning games and amazing activities there.

SPEAKER_01 10:21

And if you want to help us out, please leave us a five-star review.

SPEAKER_00 10:25

Yes. Just scroll down on whatever app you're listening on and tap those five stars. Tell us if you'd rather have a giant waving robot tower or a siren in your backyard.

SPEAKER_01 10:36

And if you want a shout out on the show like Graham, or just want to say hi, email us at hello at kidopoly.com.

SPEAKER_00 10:44

Thanks for listening, everyone. See you next time on History's Not Boring. Bye.