What you need:
A 20 cm length of 2.5 x 2.5 cm wooden baton
Electric gas appliance lighter - preferably an old one as you will need to dismantle it.
Crocodile clip or paper clips
What to do:
First make your church spire. Sharpen one end of the wooden baton into a point using either a small saw or a chisel. Make sure the other end of the baton is flat, as your Church spire will have to stand on this end.
Carefully tape a length of insulated wire along the side of the spire so that an inch pokes out top and bottom.
Strip the plastic from the ends of the wire. At the base of the wire, splay the individual strands and fold them under the spire.
Twist the strands of the bare wire at the top and leave poking up. The wire at the top should reach about 1 cm higher than the top of your pointy church spire.
Now dip your wooden spire into water.
Earth the baking tray by running an insulated wire from the tray to a cold water pipe, making sure that the wire is actually touching the metal of the pipe. I used crocodile clips to secure each end but you can use paper clips or sticky tape.
Dry off the outside of the spire and place it on the baking tray.
To make your thundercloud, scrunch up a piece of tin foil and suspend it using a cotton thread or rubber band. I built a special rig to suspend my cloud from, but you could use a chair or something similar. The cloud needs to be about 1cm above the spire.
Dismantle your electric gas-ring lighter. First slide the metal sheath off the tip; be careful that it doesn't all spring apart in your hands.
There are two metal contacts - one at the tip and one that was just covered by the metal sheath before you removed it. Take two lengths of insulated wire and run one from the contact at the tip of the electric lighter to your cloud.
Run the second wire between the other contact and the tin tray. Make sure that the joins are electrically insulated so the spark doesn't short between the two.
When you click your electric lighter now, you will charge up your cloud - so be careful not to touch the cloud, as it will zap you. Start with the wire along the side of the spire bent down and away from the tip.
Push your spire under the cloud with a wooden spoon or something else offering insulation and see if lightning strikes. It should hit the top of the spire if you keep charging up your cloud.
You may need to turn the lights down to see the spark. The tower needs to be a little bit damp otherwise you won't get a spark at all since wood is such a good insulator and your home lightning doesn't quite have the same oomph as the real stuff.
Now carefully remove the spire, fold the wire lightning rod up so that it is about 5 mm higher than the top of the spire and try lightning again. The lightning should now hit the lightning conductor in preference.
How it works:
When lightning strikes a building, it takes the path of lowest electrical resistance to the earth. In our experiment, the lightning preferred to travel down the wire rather than through the spire because the wire has less electrical resistance.
Similarly, if a building has a lightning conductor, the electrical discharge will pass down the conductor. It is worth the expense to put up a lightning conductor as otherwise the lightning will go through the spire and cause the fabric of the building to heat explosively.
Contrary to popular belief, a pointed conductor does not draw lightning to it, but is actually struck less often. The reason behind this is that a pointed conductor slowly, but continuously discharges the cloud, so the charge does not build up enough to create a flash of lightning.