This is mostly only used for very short psalms (half a dozen verses or so). The most commonly used chants are "double chants". These are twice the length of a single chant. The music of the chant is repeated for every pair of verses. This reflects the structure of the Hebrew poetry of many of the psalms: Each verse is in two halves – the second half answers the first; the verses are in pairs – the second verse answers the first. "Triple" and "quadruple chants" are considerably rarer. They appeared from the latter part of the 19th century to cover some of the exceptions to this format. They set the verses of the psalm in groups of three or four verses respectively. Psalm 2 (for example) is suited to a triple chant; a quadruple chant might be used for Psalm 78. A double chant is divided into "quarters", each of which has the music for half a verse. Triple and quadruple chants may also be described as containing six or eight quarters. If the entire text (or a section of it) has an odd number of verses, the second half of the chant is usually repeated at an appropriate point, which may be marked "2nd part". Similarly, "3rd part" markings may be used for triple chants. An example of a double chant: Below are the four lines of the doxology "Gloria Patri" (commonly known as the "Gloria"), with the text coloured to show which words correspond to which notes in the music (pointing varies from choir to choir):  Glory be to the Father, and ' to the ' Son : and ' to the ' Holy ' Ghost; As it was in the beginning, is now, and ' ever ' shall be : world without ' end A ' - - ' men. The doxology "Gloria Patri", usually sung at the end of a psalm or canticle, is two verses long. Depending on the type of chant, it is sung in one of the following ways:  Psalms may be sung unaccompanied or accompanied by an organ or other instrument. Organists use a variety of registrations to mirror the changing mood of the words from verse to verse; but the organ should never be so loud that the words cannot be clearly heard. Organists may sometimes indulge in word painting, using effects such as a deep pedal note on the word "thunder", a harsh reed tone for "darkness" contrasting with a mixture for "light", or (more frivolously!) applying the Zymbelstern to the phrases "round about" (Ps 110:10), "fair ground" (Ps 16:7) and "sea saw" (Ps 114:3).