4 years later the Parisian instrument makers Joseph and Lucien-Joseph Raoux, in collaboration with Carl Türrschmidt, came out with the cor solo, a refined version for soloists with crooks in G, F, E, E, and D. (Orchestra players needed more crooks since they needed to play in more keys). The Inventionshorn design was also applied to other brass instruments. Some examples are a pair of invention trumpets by Michael Saurle (1805) at the National Music Museum. Terminal crooks Around 1800 in France terminal crooks were invented, which proved to be extremely popular. These instruments used a separate crook for each key, and the crooks maintained a fairly uniform distance between the mouthpiece and the body of the instrument. Horn players typically needed at least eight crooks, for B-alto, A, G, F, E, E, D, and C. After about 1828, an additional crook in A-alto was also included. Although crooks for low B and B were also occasionally made, these keys were usually reached by adding couplers to the C crook. Horns constructed with the large number of crooks needed for playing in an orchestra are sometimes referred to as orchestral horns ("Orchesterhorn" in German). The main disadvantage of this system was that so many crooks needed to be transported. The large cases required for carrying them were often works of art themselves. Characteristics of manual crooks According to John Humphries' The Early Horn, A Practical Guide: The discovery of crooks is usually a great and unexpected pleasure to performers who have previously used only modern double horns, for they differ greatly in timbre and response. The highest keys, B and A, are very focused and penetrating in tone, and respond quickly, making rapid tonguing easy, but they soon become tiring to play because they are usually used for very high parts. At the opposite end of the spectrum, the low B and C crooks have a rich, dark almost muddy tone, but, because of their length — B has 18 feet (about 5.5m) of tubing — are slow to speak. Indeed, the difference in response between a horn crooked in B alto and one in B basso is akin to the difference in handling between a sports car and a lorry. The invention of valves The use of crooks in conjunction with hand-stopping made the horn into an almost completely chromatic instrument, but the change in timbre associated with stopped