On long instruments with a narrow mean diameter like the natural trumpet and the natural horn of Bach's time, highly accomplished musicians can reach up into the fifth octave, up to the 28th natural note, by applying the correct lip tension and air pressure.
It is possible to expand the original range of the harmonics by using technical devices, such as adding several crooks, by partial occlusion of the bell with the hand ('hand-stopping' with the French horn) or by adding keys to the instrument.
Chromatic notes and therefore a complete scale make it possible for these instruments to be played together with other musical instruments.
Originally the additional crooks were placed above the body of the instrument. But in the late 18th century, they were also placed by hand in the middle of the instrument.
('lnventionshorn' or 'Invention' trumpet).
The valve mechanisms which were developed from 1814 onwards and then patented in 1818 made it possible to gain mechanically access to the built-in crooks (valve instruments).