Trombone
2 of the 7 encyclopedias on this shelf carry an entry for Trombone. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a large, deep, and loudtoned instrument of the trumpet kind, the name being an augmentative of tromba, a trumpet. It consists of two tubes, so constructed that one may slide in and out of the other, and thus form one tube that can be lengthened at will and made of varying pitch. There are three kinds of trombones, called after their compass the alto, tenor, and bass trombones. Soprano trombones have also been made, but they are rarely used. The alto trombone has a compass of more than two octaves and a half, and is also known as the trombone in E flat. It is written on the c clef, third line. The tenor trombone is also known as the trombone in B flat. It is written on the c clef, fourth line. The bass trombone is the lowest of all in its range of notes, and is known as the E flat. It is written on the F clef; is an octave lower than the alto, and a fifth lower than the tenor. Some of these instruments are fitted with pistons, whence they are called valve trombones. Also a powerful reed stop in the organ, of 8 feet or 16 feet scale on the manuals and 16 feet or 32 feet on the pedals. In ordnance, a form of blunderbuss for boat service.
Aiton's Encyclopedia (1910)
a large musical instrument of the trumpet kind. It has a long tube bent twice upon itself. One of the loops is double. The player slides it in and out to change the pitch of his notes. When the loop slides out the tube is lengthened and the note is lowered. The change of length covers a full octave. The tone of the trombone is rich and impressive. It is a favorite instrument in an orchestra or military band. See Orchestra