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Jonahan Hare's Diary

Seismograph

SeismographKathy and I modify the clock and try several ways to improve the quality of the pen / writing surface. End up soldering an additional arm to the min hand so that the paper is supported fully. This works much better.

Jonathan, Kathy and Ellen at the quarryWe take all the equipment to the quarry about an hour away from the sawmill and set up the seismograph on the road. The two quarry men who are looking after us drill two large holes in the ground and we fit the base of the seismograph to these holes using two metal poles rammed in. Set up the pendulum and the clock and try a test run – but with no earthquake! The clock chart recorder makes a beautiful line and we know that everything is working very well, in fact the best it has worked so far.

Ellen has made up a really nice shelter for the seismograph consisting of a wooden structure to hold a homemade roof.

Then the Helicopter with the two Mikes comes over and drops them off with us so that we can film the end of the program sequence at the quarry. As the helicopter comes in the air blast moves the seismograph pen clean off the chart recorder very spectacular!! The Two Mikes look tired but very happy they obviously had a great time up on the mountain.

All of us get together for the official blasting and testing of the seismograph. The quarry men set up a charge some distance from the instrument and we huddle far off at the end of the wire detonator. As Kate turns the key to explode the charge there is a great blast, we feel the air blast in our stomachs and the rumblings continue for sometime as the sound echoes from hill and mountain to hill and mountain. Then we run off down to the instrument to see what it has recorded.

Straight line on the seismographKathy and I are amazed, in fact everyone is amazed – there is absolutely nothing registered on the seismograph just a nice straight line!! We have made the most insensitive device that you can imagine!! So what's going on? We do another charge and the same thing happens!

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Then we question the quarry men as to how they are setting up the charge and they tell us that they laid the dynamite on the rock surface rather than into a hole into the rock. The results now seem to make sense as this situation would make a lot of noise but not expect to move the rock much. So they drill a hole near to the instrument and load a charge into it. Now finally in this test we manage to record something – a tiny blip on the chart recording! Evidently it is much harder to make the earth move than you might think!!

The Rough Scientists at the end of challenge threeActually this does make sense. An earthquake really does move the earth by cm's even many kilometers from the source of the quake. A little stick of dynamite would not be expected to move such a large amount of rock. But then I heard stories that even blasting going on in other quarries far off set their seismographs moving, how so? Well most modern day instruments work on similar principles to ours but they have electronics to amplify the sensitivity many 1000 of times. Our machine registers mm's of movement on the rocks, which is not very likely but amplify this so that you can measure millionth of a meter and you would detect all sorts of vibrations and natural earth movements even many kilo meters away. So our instrument did work but it was not sensitive enough to detect dynamite only earthquakes!

A spectacular but also slightly un eventful end to TV3.

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Photo: Jonathan Hare
Metal Detector Interactive