fourth, like the third, is a use scarcely found except in the older writers. The word “bond” is of course a mere translation of obligatio. Obligations may be either perfect or imperfect. A perfect obligation is one which is directly enforceable by legal proceedings; an imperfect or moral obligation (the naturalis obligatio of Roman law) is one in which the vinculum juris is in some respects incomplete, so that it cannot be directly enforced, though it is not entirely destitute of legal effect. A perfect obligation may become imperfect by lapse of time or other means, and, conversely, an imperfect obligation may under certain circumstances become perfect. Thus a debt may be barred by the Statute of Limitations and so cease to be enforceable. The obligation, however, remains, though imperfect, for if there be a subsequent acknowledgment by the debtor, the debt revives, and the imperfect obligation becomes again perfect. At one period there was some doubt among English lawyers whether a moral obligation could be regarded as sufficient consideration for a contract; it has now, however, been long decided that it cannot be so regarded.
American law is in general agreement with English, except in the case of Louisiana, where the terms obligor and obligee are used in as wide a sense as the debitor and creditor of Roman law. By art. 3522 of the Louisiana civil code obligor or debtor means the person who has engaged to perform some obligation, obligee or creditor the person in favour of whom some obligation is contracted, whether such obligation be to pay money or to do or not to do something. The term obligation is important in America from its use in art. i. s. 10 of the constitution of the United States, “No state . . . shall pass any . . . law . . . impairing the obligation of contracts.” This does not affect the power of Congress to pass such a law. Contracts between private individuals are of course within the provision. So are private conveyances, charters of private corporations and statutory and other grants by a state. On the other hand, marriage and divorce, and arrangements which are political in their nature, such as charters of municipal corporations, licences to carry on particular trades or regulations of police are not within the provision. In order to fall within it, the law must act upon the terms of the agreement, and not merely upon the mode of procedure. If it act not upon the terms but upon the remedy, it impairs the obligation if it purport to be retrospective, but it is valid so far as it applies to subsequent contracts.
OBNOXIOUS (Lat. obnoxiosus, from ob, over, against, and noxa, harm), a word originally meaning “exposed to harm or injury,” but now “exciting aversion or dislike.” The current use dates from the later 17th century.
OBOE, or Hautboy (Fr. hautbois, Ger. Hoboe, Ital. oboe),
the treble member of the class of wood-wind instruments, having
a conical bore and a double reed mouthpiece. The oboe consists
of a conical wooden tube, composed of three joints, upper,
middle and bell, and of a short metal tube to which are bound
by many turns of waxed silk the two thin pieces of cane that form
the mouthpiece. These pieces of cane are so bevelled and
thinned at the end which is taken into the mouth that the
gentlest stream of compressed air suffices to set them vibrating.
Practice has demonstrated that the reed stalk of which the
double reed mouthpiece is made, should not be of narrower
internal diameter than the pipe containing the column of air
upon which it is destined to act. The player breathes gently
into the aperture, which has the form of a very narrow ellipse,
managing his breath as for singing. The vibrations of the double
reed produce in the stream of compressed air issuing from the
player’s lips the rhythmical series of pulses necessary to generate
sound waves in the stationary column of air within the main tube
of the instrument.
 |
| Rudall, Carte & Co. |
| Fig.1.—The Oboe. |
In the upper and middle joints are the rings and keys covering lateral holes bored through the tube, by means of which the column of air, and consequently the wave length, may be shortened at will; the bell joint contains one or two keys normally open, which when closed extend the lowest register by lengthening the air column. These holes and keys produce the fundamental scale of the oboe, which possesses notes sufficient for an octave with all chromatic intervals. The next octaves are obtained by means of cross fingering (Fr. doigté fourchu, Ger. Gabelgriff), and of the octave keys, which do not give out an independent note of their own, but determine a node in the column of air, whereby the latter divides and vibrates in two half sections producing the second harmonic overtone or octave. In order to obtain this result the player increases the pressure of his breath and also the tension of his lips against the reed.
The compass of the oboe is from 
with all
chromatic semitones. The G clef is used in notation and all
notes are sounded as written.
The quality of tone or timbre depends primarily on the configuration of the sound waves (see Horn), which is influenced by the special characteristics of the mouthpiece: the musical tone of an instrument may be said to be due more directly to the prevalence and relative strength of the many harmonics which go to make up a composite tone or clang. The quality of the oboe tone resembles that of the E string of the violin, but is more nasal, more penetrating and shriller. The lower register is thin and somewhat sweeter, approximating to the upper register of the cor anglais. But the timbre does not vary appreciably in the different registers, and to this want of variety in tone colour is due the unpopularity of the oboe as a solo instrument, although it is invaluable as a melody-leading instrument in the orchestra, balanced by clarinets and flutes. The oboe lends itself admirably to pastoral music. The technical capabilities of the instrument are very varied. It is possible to play on it diatonic and chromatic scale and arpeggio passages, legato and staccato; leaps; cantabile passages; sustained notes, crescendo and diminuendo, grace notes and shakes (with reservations). The keys having many sharps and flats are the most difficult for the oboist.
The double reed is the most simple, as it is probably the oldest, of all reed contrivances. It is sufficient to flatten the end of a wheat straw to constitute an apparatus capable of setting in vibration by the breath the column of air contained in the rudimentary tube; the invention of this reed is certainly due to chance. An apparatus for sonorous disturbance thus found, it was easy to improve it: for the wheat stalk a reed stalk was substituted, and in the extremity of its pipe another reed stalk much shorter in length was inserted, pared and flattened at the end; and then came the lateral holes, probably another discovery of the great inventor chance. For the reed tube a wooden one was substituted, still preserving the reed tongue, and it is in this form, after having played an important part amongst the sonorous contrivances of antiquity, that we find the ancestor of the oboe playing a part no less important in the 16th century, in which it formed the interesting families of the cromornes, the corthols and the cervelas. All these families have disappeared from the instrumental combinations of Europe, but they are still to be found in Eastern wind instruments, such as the Caucasian salamouri, the Chinese kwantze, and the hitshiriki of Japan.
It is impossible to say when it was that man first employed the
phenomena of double reeds and conical pipes, but the knowledge of
them must at least have been later than that of the cylindrical
pipe, which we may regard as directly furnished by nature. That
antiquity made use of them, however, has been proved by Gevaert
in his admirable Histoire de la musique dans l’antiquité; but this
learned author states that the double-reed pipes held but an insignificant
place in the instrumental music of ancient Greece and
Rome, a statement which is open to challenge (see Aulos).
