Bessler demanded 20 thousand pounds (about 100 thousand Reichstalers, if you transfer the amount into the currency of that time) for the secret of his invention. Peter the First showed great interest in the invention and asked Wilhelm Gravesand, professor of mathematics and astronomy at Leiden University, to advise him before buying a “perpetuum mobile.” Johann Bessler decided that the secret of the “perpetual motion machine” was to be stolen, and destroyed his invention.