Ancient chair why is the front low back high?

Chair is the essence of China's classical furniture of the Ming and Qing dynasties, "official hat chair" is the most popular varieties of traditional Chinese chairs.　　The so-called "official hat chair", usually including "four out of the head of the official hat chair" and "south official hat chair". The former refers to the back of the chair on the brain of the two ends and two armrests are out of the head of the modeling, this chair style and the ancient officials wore a hat similar, so it is called "four out of the head of the official hat chair". Such chair back post and legs are through the chair plate with a wood made of front legs and armrests under the neck of the goose is also mostly a wooden joint do; there is also a goose neck back into the chair plate, the upper and lower does not communicate with the practice. Chair armrests and chair plate more than thin under the thick even help stick, chair plate under all kinds of different teeth decorations. Chair back, armrests, goose neck, even help the stick and other components more S-shaped, is typical of Ming furniture. "South official hat chair" should be "four out of the head of the official hat chair" a kind of improvement, its head and armrests are not out of the head, is generally believed to have appeared in the end of the Ming Dynasty. Su (state), Song (Jiang) area of the literati very much like to use this chair does not come out of the head, like to place it in pairs in the study side of the window, so the world known as the "South Hat Chair" or "Wen Chair". The "South official hat chair" is divided into two categories: a high back modeling, is the "four out of the head of the official hat chair" continues. Its shape and size of the basic and "four out of the head of the official hat chair" the same, but the brain, armrests are not out of the head. But the back of the brain was lowered to the lower part of the shoulders, while the armrests and the back of the two columns of the mortise and tenon point moved up inches, forming the armrests after the high front of the low situation, more suitable for the sitter's hands on the support.