18th century printing conventions: Use of italics?

[No_Wikipedia_Cites]

In poetry printed in the eighteenth century, italics are used on key words. What were the actual rules for using italics in this manner?

Let Hist’ry tell where rival Kings command,
And dubious Title shakes the madded Land,
When Statutes glean the Refuse of the Sword,
How much more safe the Vassal than the Lord,
Low sculks the Hind beneath the Rage of Pow’r,
And leaves the* bonny Traytor *in the Tow’r,
Untouch’d his Cottage, and his Slumbers sound, [35]
Tho’ Confiscation’s Vulturs clang around.

From every Room descends the painted Face,
That hung the bright *Palladium * of the Place,

(Vanity of Human Wishes)

I see that Britain is always capitalized.
In Rape of the Lock (Title of poetry, modern printing convention!) we have

What dire Offence from am’rous Causes springs,
What mighty Contests rise from trivial Things,
I sing — This Verse to C——, Muse! is due;
This, ev’n *Belinda *may vouchfafe to view:
Slight is the Subject, but not so the Praise,
If She inspire, and He approve my Lays.
Say what strange Motive, Goddess! cou’d compel
A well-bred *Lord *t’assault a gentle Belle?
Oh say what stranger Cause, yet unexplor’d,
Cou’d make a gentle *Belle *reject a Lord?
And dwells such Rage in softest Bosoms then?
And lodge such daring Souls in Little Men?

http://andromeda.rutgers.edu/~jlynch/Texts/rapelock.html

Ok, Belinda and Lord, and Belle are in italics; but why not Goddess?

Later it reads:

Now move to War her Sable Matadores,
In Show like Leaders of the swarthy Moors.
*Spadillio *first, unconquerable Lord!

Notice now the Lord is unitalicized;

Is this a strict rule, or just for effect? It seems to be used on countries and proper names; can it also be used like boldface to call attention whereever the writers wishes?

[Giles]

My guess is that italics were being used for names for people and places – words which we would mark with capital letters today. In the 18th century, capital letters were used for all nouns (as with German today), so italics are being used as a extra mark for proper nouns.

In “Cou’d make a gentle Belle reject a Lord?” both “Belle” and “Lord” refer to specific people (the lady with the locks, and the lord who raped them). On the other hand, in “unconquerable Lord” the “Lord” is not a specific person – it’s actually a playing card, in the spade (“Spadillio”) suit.

[BigT]

While not what is being used there, it was also sometimes used in translations to indicate a word was not in the original. It was probably a carryover from the rule that required this in the King James Version of the Bible, a book with which most scholars were quite familiar.

That said, Guile’s guess is beguiling*, because we do that now with bold in places where some names do not require capitals.

*Pun very much intended. I don’t think the word is usually used that way.

[CalMeacham]

I’ve copied some 18th century titles and cover pages – all wordy and with plenty of italics – and have come to the conclusion that it’s all up to the printer’s or typesetter’s fancy and discretion. I can frequently find neither rhyme nor reason to their choices for italicization. They always do it to words they want to emphasize, or course, but they seem to do it to other words at random. And they also avoid italicizing other words that ,if I were setting the type, would definitely be.