 The remedy for this limitation was the use of crooks, i.e., sections of tubing of differing length that, when inserted, altered the length of the instrument, and thus its pitch.In the mid-18th century, horn players began to insert the right hand into the bell to change the length of the instrument, adjusting the tuning up to the distance between two adjacent harmonics depending on how much of the opening was covered.In 1818 the German makers Heinrich Stölzel and Friedrich Blümel patented the first valved horn, using rotary valves.