piston returns by the action of a spring.  In large bass and contralto instruments, a fourth piston is added, which lowers the pitch two tones and a semitone.  By combining the use of three valves, lower notes are obtained—­thus, for a major third, the second is depressed with the third; for a fourth, the first and third; and for the tritone, the first, second, and third.  But the intonation becomes imperfect when valves are used together, because the lengths of additional tubing being calculated for the single depressions, when added to each other, they are too short for the deeper notes required.  By an ingenious invention of compensating pistons, Mr. Blaikley, of Messrs. Boosey’s, has practically rectified this error without extra moving parts or altered fingering.  In the valve section, each altered note becomes a fundamental for another harmonic scale.  In Germany a rotary valve, a kind of stop cock, is preferred to the piston.  It is said to give greater freedom of execution, the closeness of the shake being its best point, but is more expensive and liable to derangement.  The invention of M. Adolphe Sax, of a single ascending piston in place of a group of descending ones, by which the tube is shortened instead of lengthened, met, for a time, with influential support.  It is suitable for both conical and cylindrical instruments, and has six valves, which are always used independently.  However, practical difficulties have interfered with its success.  With any valve system, however, a difficulty with the French horn is its great variation in length by crooks, inimical to the principle of the valve system, which relies upon an adjustment by aliquot parts.  It will, however, be seen that the invention of valves has, by transforming and extending wind instruments, so as to become chromatic, given many advantages to the composer.  Yet it must, at the same time, be conceded, in spite of the increasing favor shown for valve instruments, that the tone must issue more freely, and with more purity and beauty, from a simple tube than from tubes with joinings and other complications, that interfere with the regularity and smoothness of vibration, and, by mechanical facilities, tend to promote a dull uniformity of tone quality.

Owing to the changes of pitch by crooks, it is not easy to define the compass of the French horn.  Between C in the bass clef and G above the treble will represent its serviceable notes.  It is better that the first horn should not descend below middle C, or the second rise above the higher E of the treble clef.  Four are generally used in modern scores.  The place of the horn is with the wood wind band.  From Handel, every composer has written for it, and what is known as the small orchestra of string and wood wind bands combined is completed by this beautiful instrument.