1925—Edgar Kelley, in his text on musical instruments, says the following about trombone

“This noble instrument…was the only brass instrument capable of producing all the tones of the chromatic scale. But the classical composers rarely took advantage of this fact, and not until Schubert’s time were its manifold possibilities exploited….The trombone has a vast dynamic range from the pianissimo in the scene where Siegfried climbs the rocks to find Brünnhilde to the glorious fortissimo outburst (combined with Trumpets) when Tannhäuser tells of the pardoning of sinners by the Pope (Kelley 190).