
Jane Austen (wikipedia)
The first letter by Jane Austen that has come down to us, addressed to her sister Cassandra, ends as follows:
I condole with Miss M. on her losses and with Eliza on her gains, and am ever yours,/J. A. (letter 1, ed. Le Faye 2011:3).

Cassandra Austen (wikipedia)
In the correspondence, it is very unusual, even in the letters to Cassandra, which are the most intimate ones in the collection: there is only one other instance besides this one, in letter 61. I have never come across this formula in 18th-century letters before, though reading Annemiek Korf’s MA thesis on John Wesley‘s letters to his wife, I discovered that Wesley used the form too, though only once.
So how common was this form in Late Modern English? Do we only find it in love letters, like Wesley’s, or is it also common in letters between correspondents who were extremely close, such as Jane Austen and her sister Cassandra?
Reference:
Le Faye, Deirdre (2011), Jane Austen’s Letters [4th ed.]. Oxford: Oxford University Press.
Annemiek Korf is one of the contributors to this blog.