'Thunder house', c 1740-1770.
© Science Museum / Science & Society Picture Library
This instrument was made by George Adams, instrument maker to the king, to demonstrate the action of lightning conductors. An electric spark jumped between the two balls above the house, imitating a lightning strike. If the lightning conductor was in place the charge was earthed safely. However, a small piece of the conductor could be removed and replaced in the wrong position. If the house was struck again this piece would jump out, representing damage.