In passing it is necessary to refer to the structure of Chinese verse, which, difficult as it is to grasp and differing in particulars from our European ideas of technique, has considerable interest for the student of verse form and construction.
The favourite metres of the T`ang poets were in lines of five or seven syllables. There is no fixed rule as regards the length of a poem, but, generally speaking, they were composed of four, eight, twelve, or sixteen lines. Only the even lines rhyme, except in the four-line or stop-short poem, when the first line often rhymes with the second and fourth, curiously recalling the Rubaiyat form of the Persian poets. There is also a break or caesura which in five-syllable verses falls after the second syllable and in seven-syllable verses after the fourth. The Chinese also make use of two kinds of tone in their poetry, the Ping or even, and the Tsze or oblique.
The even tone has two variations differing from each other only in pitch; the oblique tone has three variations, known as "Rising, Sinking, and Entering." In a seven-syllable verse the odd syllables can have any tone; as regards the even syllables, when the second syllable is even, then the fourth is oblique, and the sixth even. Furthermore, lines two and three, four and five, six and seven, have the same tones on the even syllables. The origin of the Chinese tone is not a poetical one, but is undoubtedly due to the necessity of having some distinguishing method of accentuation in a language which only contains about four hundred different sounds.