The Touchstone is a device that can control the weather on a planetary scale.
The Touchstone is a statuette, with the upper part being a small sphere surrouned by three rings. By aligning this rings in different positions, the weather can be changed as seen fit. The device can be completely reset by aligning all three rings vertically.
About 900 years ago, the planet Madrona was terraformed by an unknown alien culture, making it habitable for humans. These aliens then probably left behind the Touchstone which became essential to maintain a stable weather on the planet. If it is removed, the weather quickly turns into a blizzard. When the Madronans settled on this planet, they began to use the Touchstone to maintain a pleasant weather at all times. The device was placed in the hands of a statue and controlled by a high priest.
After SG-1 visited the planet, the device was stolen by rogue NID agents, who brought it to Earth where they experimented with it. However due to the fact, that the device was specifically tuned for Madrona, strange climate changes occurred on Earth (including record floods in unlikely areas). Thanks to this, SG-1 was able to locate the Touchstone and bring it back to Madrona, where the high priest quickly reset the weather. (SG1: "Touchstone")
Behind the scenesEdit
It is hinted in the book Stargate SG-1: Friends and Foes: Stargate Season Two that the unknown aliens who terraformed the planet were the mysterious Furlings and that the Touchstone is one of their technology.