Question about the use of 中 (first or fourth tone)?
it's zhōng, according to 國語辭典:

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000120693

in cantonese, it jung1 (sydney lay scheme)

http://humanum.arts.cuhk.edu.hk/Lexis/lexi-mf/search.php?word=中

sound file: http://humanum.arts.cuhk.edu.hk/Lexis/lexi-mf/sound/zung1.Mp3

方者﹒才也﹒始也; roughly "only then"

have fun :)