PRONOUNS, RELATIVE AND INTERROGATIVE. Which for "as to which"Which for "as to which." Hence which and "the which" are loosely used adverbially for "as to which." So in Latin, "quod" in "quod si."
“Showers of blood,
The which how far off from the mind of Bolingbroke
It is such crimson tempest should bedew, &c.
“With unrestrained loose companions--
Even such, they say, as stand in narrow lanes,
And beat our watch, and rob our passengers;
Which he, young, wanton, and effeminate boy,
Takes on the point of honour, to support
So dissolute a crew.
“But God be thanked for prevention;
Which I in sufferance heartily will rejoice.