Final answer:
By the 19th century, valves were used in the design of trumpets to improve pitch control, allowing for a broader range of notes and a richer musical expression.
Step-by-step explanation:
By the opening of the 19th century, we find that valves were used to cover holes along the trumpet tubing.
This development in the design of wind instruments allowed for more precise control over the pitch of the notes played.
The introduction of valves was essential in transforming the trumpet from a natural horn with limited notes into a fully chromatic instrument capable of playing a wide range of pitches.
Before the valve system was integrated, changing the pitch was primarily achieved by altering the embouchure or by inserting hand-stoppers into the bell of the horn.
With the addition of valves, the length of the resonating air column within the trumpet could be changed swiftly and accurately by the musician, providing a richer musical expression and enabling the performance of complex musical pieces.