<p>What is Heng's Dragon Jar and what has it got to do with earthquakes?</p>.<p>The world’s first ‘seismoscope’ was invented way back, almost 2000 years ago in China. In 132 AD, Chang Heng invented what is now called the Dragon Jar. No known sample of it exists, but Chang Heng fortunately wrote about his invention, and so did many other historians of that period. And for a span of 400 years, this bronze jar with a 6 ft diameter, actually recorded earthquakes that occurred within a radius of over 400 kilometres.<br /><br />On the shoulder of the outside of this jar were 8 dragon heads, each with a bronze ball held precariously within its jaws. The 8 dragons represented the 8 directions on a compass (to measure in which direction the quake occurred). <br /><br />Directly below each dragon was an open-mouthed frog. If an earthquake occurred, it dislodged the ball in a particular dragon’s mouth, resulting in its frog partner getting a meal. Which is why I’ve taken the liberty of coining an “ancient” Chinese proverb: When dragons feed frogs, somewhere the Earth has shuddered! <br /><br />In one documented case, Chang Heng reported the occurrence of an earthquake that nobody in his town had felt….till a messenger arrived a few days later from a town 400 miles away, to report an earthquake!<br /><br />During the 1800s and 1900s when the study of the earth became more scientific with branches like geology and seismology beginning to evolve, people tried recreating Heng’s jar. But nobody knew how he had designed the insides. Scientists can only speculate that this jar must have worked on the principle of the pendulum.<br /><br />In the 1880s, British geologist and seismologist, John Milne, invented the horizontal pendulum-based seismograph. And he, along with other Japanese and British scientists turned Japan, a country that’s continually being jolted by earthquakes into a sort of large laboratory to study the Earth’s movements. Soon a seismology station was opened in Japan, followed by others across the world.<br /><br />DIY seismograph <br /><br />There will be no need for dragons and frogs! All you’ll require are:<br />* A light-weight, square box, with sides that need to be about 15-20 cm high<br />* Non-hardening modelling clay<br />* Cello tape<br />* A felt-tipped pen (the sides of your box have to be taller than this pen)<br />* String<br />* A pencil<br />* A piece of card<br /><br />If your box has a lid, discard it; if it has those 4 folds that make up the 4th side of a box, cut them away as you need just 3 sides. On the side marked ‘A’, use a pencil or compass tip to make a hole big enough to pass a thick string through.<br /><br />Leave that box aside for a while. Use a fair amount of clay to knead and mould a heavy ‘ball’ around the felt pen, as shown. Now tie a string to the back end of the felt pen and pass that through the hole in the box you’d made earlier. Wind the other end of the string around a pencil, as shown. After setting up the box, twirl the pencil such that the felt pen is suspended with just its tip touching the floor of the box. Secure the pencil with tape so it doesn’t ‘un-twirl’. Slip a bright piece of card just below the felt tip.<br /><br />Now, simulate an earthquake! Place your seismograph on a table and gently push the table. If your shove was very mild, the box might move, but the heavier ‘pendulum’ or felt-pen-with-clay-ball, will NOT! Because its inertia is higher than that of the box. It also means that seismographs will not measure all the minute shifts of the earth’s tectonic plates (which are moving all the time), but only the more dramatic movements that constitute an ‘earthquake’.<br /><br />When you push the table with a little more force, your pendulum will move, and the arc it draws on the coloured card, will depend on the ‘magnitude’ of the earthquake you created! There, you now have your own seismograph.<br /><br />The Richter scale<br /><br />This is not really a ‘scale’ that you can see or use like a weighing scale. Rather, it is a set of calculations that seismologists across the world use to rate the magnitude of an earthquake. It was first formulated by Charles Richter in 1935, in California. The ‘magnitude’ of an earthquake refers to the amount of energy released at its epicentre…this is scientifically calculated.</p>
<p>What is Heng's Dragon Jar and what has it got to do with earthquakes?</p>.<p>The world’s first ‘seismoscope’ was invented way back, almost 2000 years ago in China. In 132 AD, Chang Heng invented what is now called the Dragon Jar. No known sample of it exists, but Chang Heng fortunately wrote about his invention, and so did many other historians of that period. And for a span of 400 years, this bronze jar with a 6 ft diameter, actually recorded earthquakes that occurred within a radius of over 400 kilometres.<br /><br />On the shoulder of the outside of this jar were 8 dragon heads, each with a bronze ball held precariously within its jaws. The 8 dragons represented the 8 directions on a compass (to measure in which direction the quake occurred). <br /><br />Directly below each dragon was an open-mouthed frog. If an earthquake occurred, it dislodged the ball in a particular dragon’s mouth, resulting in its frog partner getting a meal. Which is why I’ve taken the liberty of coining an “ancient” Chinese proverb: When dragons feed frogs, somewhere the Earth has shuddered! <br /><br />In one documented case, Chang Heng reported the occurrence of an earthquake that nobody in his town had felt….till a messenger arrived a few days later from a town 400 miles away, to report an earthquake!<br /><br />During the 1800s and 1900s when the study of the earth became more scientific with branches like geology and seismology beginning to evolve, people tried recreating Heng’s jar. But nobody knew how he had designed the insides. Scientists can only speculate that this jar must have worked on the principle of the pendulum.<br /><br />In the 1880s, British geologist and seismologist, John Milne, invented the horizontal pendulum-based seismograph. And he, along with other Japanese and British scientists turned Japan, a country that’s continually being jolted by earthquakes into a sort of large laboratory to study the Earth’s movements. Soon a seismology station was opened in Japan, followed by others across the world.<br /><br />DIY seismograph <br /><br />There will be no need for dragons and frogs! All you’ll require are:<br />* A light-weight, square box, with sides that need to be about 15-20 cm high<br />* Non-hardening modelling clay<br />* Cello tape<br />* A felt-tipped pen (the sides of your box have to be taller than this pen)<br />* String<br />* A pencil<br />* A piece of card<br /><br />If your box has a lid, discard it; if it has those 4 folds that make up the 4th side of a box, cut them away as you need just 3 sides. On the side marked ‘A’, use a pencil or compass tip to make a hole big enough to pass a thick string through.<br /><br />Leave that box aside for a while. Use a fair amount of clay to knead and mould a heavy ‘ball’ around the felt pen, as shown. Now tie a string to the back end of the felt pen and pass that through the hole in the box you’d made earlier. Wind the other end of the string around a pencil, as shown. After setting up the box, twirl the pencil such that the felt pen is suspended with just its tip touching the floor of the box. Secure the pencil with tape so it doesn’t ‘un-twirl’. Slip a bright piece of card just below the felt tip.<br /><br />Now, simulate an earthquake! Place your seismograph on a table and gently push the table. If your shove was very mild, the box might move, but the heavier ‘pendulum’ or felt-pen-with-clay-ball, will NOT! Because its inertia is higher than that of the box. It also means that seismographs will not measure all the minute shifts of the earth’s tectonic plates (which are moving all the time), but only the more dramatic movements that constitute an ‘earthquake’.<br /><br />When you push the table with a little more force, your pendulum will move, and the arc it draws on the coloured card, will depend on the ‘magnitude’ of the earthquake you created! There, you now have your own seismograph.<br /><br />The Richter scale<br /><br />This is not really a ‘scale’ that you can see or use like a weighing scale. Rather, it is a set of calculations that seismologists across the world use to rate the magnitude of an earthquake. It was first formulated by Charles Richter in 1935, in California. The ‘magnitude’ of an earthquake refers to the amount of energy released at its epicentre…this is scientifically calculated.</p>
