Let's kick off with a text from the middle of the 19th century:
From four to six pounds, per quarter of malt, is sufficient ;—if for ales, the sweetest hops should be used. Boil half the quantity of hops with the first wort twenty minutes, before drawing from the copper; the other half in like manner, with the second wort, without those boiled with the first wort. The third wort, if any, may have the whole hops of the two former worts boiled with it the same length of time. By boiling the hops in this manner, their aroma and fine bitter are retained, which are lost by long boiling; nor does long boiling appear to produce more bitter.
When a particularly fine bitter is desired, the whole of the hops may be placed in the hopback, (such as is herein recommended,) on the false bottom, and the boiling wort run on them, and allowed to remain a quarter of an hour, keeping the hopback covered close. This is decidedly the best way of extracting the finer qualities of the hops."
"A practical treatise on brewing" by Thomas Hitchcock, 1842, pagess 29-30.
Wasn't that interesting? Half the hops boiled for 20 minutes in the first copper, the other half boiled for 20 minutes in the second, then both sets of returned hops boiled for 20 minutes in the third copper.
The second method is even more intriguing: not boiling the hops at all, just infusing them in the hot wort in the hop back. Surely that's a really wasteful way of hopping?
Now a somewhat older method, back from the pre-scientific days of brewing:
I have heard of this one before. Putting the hops in a bag, boiling them for half an hour, then taking them out and putting fresh hops in the bag. There were some in the 18th century who maintained that you should nver boiled hops for more than 20 minutes. At least not for full-strength beer. Small Beer just got second-hand, pre-boiled hops.
If the beer be intended for keeping, half a pound of fresh hops should be put in every half hour, and the whole boiled briskly for an hour and an half. While this first copper of wort is boiling, some scalding hot water must he poured in upon the malt, bowl by bowl; and ,thus so much, is to be got in and suffered to run off again, that there may be the quantity of another copper ready for boiling, by that time the first quantity is boiled off.
When this is drawn off the second running must be put in and boiled an hour, with nearly the same quantity of hops as at first; and while this is doing, preparation may be making for small beer, by pouring on such a quantity of water as the farmer chuses, cold upon the grains all at once, or at twice. This must be boiled in the copper in the same manner as the ale wort, and must have the hops that were boiled before. Each copper of the small beer should be allowed an hour in boiling"
"A compleat body of husbandry, Volume 3" by Thomas Hale, 1758, pages 325-326.
This isn't getting dull, is it? You would tell me, wouldn't you?