《论衡·卷十一·谈天篇》
北斗星下的地方的北面有五万里，那么北斗星下的地方的东面与西面也都该各有五万里。
极北亦五万里，极东西亦皆五万里焉。
If the north side of the place below the Big Dipper is fifty thousand li, then the east side and the west side of the place below the Big Dipper should each be fifty thousand li. 