A question that comes up periodically is that of why was the valve invented. There is a myth that is repeated often that they were invented as a crook changing device and only later did players realize that they could use them to play chromatic passages. Myth? Yes, this is absolutely a myth. I wrote an extended article on the topic for The Horn Call of which a version is still in my Horn Articles Online site. Check out the full article, but this is the money quote, direct from hornist Heinrich Stoelzel himself in a letter written to the King of Prussia in December of 1814.
My horn can play all the notes from the lowest to the highest with the same purity and strength without having to stop the hand into the bell. The mechanism of my invention is most simple, can be employed easily and quickly and everyone who plays the instrument can make himself thoroughly familiar with its application in a few days. This device renders the many crooks superfluous and makes it possible for the artist to play all the notes without losing any of the instrument’s tone. This mechanism can also be applied to the far more imperfect trumpet and even to the bugles. Because the trumpet, whose compass hitherto consisted of 13 notes and through my invention has received 24 additional notes, which sound just as beautiful and pure as those 13 and for which now composers may write in not so limited fashion, but in any major or minor key as they wish, I believe that I do not exaggerate in promising your Majesty that by means of these instruments music may be made which will astound the world.
That one quote pretty much puts the nails in the coffin of the myth so far as I am concerned, a topic I did research out pretty thoroughly. I think part of what happened is players looked at some of the odd notations in some horn parts of Wagner (especially Lohengrin) and thought that he was maintaining some old form of notation that came from the earliest valved horn players. Actually, Wagner was out in left field! That is a topic for another day but for those researching horn notations in Wagner I suggest a reading of my article, “Joseph Rudolphe Lewy and Valved Horn Technique in Germany, 1837-1851,” The Horn Call Annual 9 (1997), 23-35, which covers this angle of the topic in great depth.