The innovation of the double slide took place in 1816, proposed by Gottfried Weber in which he described its construction. In 1830 the first double-slide trombone was produced (pitched in F with very short slide positions) by Halary in Paris. The slide was wound back on itself to produce four tubes, each of which moved in tandem with its partner and halved the usual length of the slide shifts. During this time, the contrabass trombone enjoyed a revival and it was constructed according to the double slide principle. As with developments in the other members of the Trombone family at the time, the bores were enlarged and bell flares were widened to give a more broad, darker tone. The application of valves was first applied to the Tenor and Bass Trombones, with the older bass in F being replaced by a horn pitched in B with F and D triggers. At the turn of the 20th century, Conn manufactured a small number of contrabass trombones, of which three are known to survive.