I have been wanting to respond to Helen Battersby's perceptive posting tracing the changes in tone and attitude we find in Mary's letters from London to Fanny. Helen showed us that Mary ever so gradually falls away from the depth of individual feeling and imaginative musings we find her expressing in her last interview with Fanny in Fanny's attic as Fanny's attic awakens her memories of childhood and the whole of her time at Mansfield (Mansfield Park Chapman III:5, 358-64; Penguin Ch 36, pp 354-9) to the strained coquetry and pragmatic arguments of her last interview with Edmund (Mansfield Park ChapmanIII:16, 454-59; Penguin Ch 47, pp 440-45). The points I'd like to add are that Mary's letters are interlaced with Edmund's and both sets of letters also tell the story of the gradual involvement of Henry with Maria in London and their elopement.
I'll deal with the second element in Mary's letters first. There are 4 letters not three, and each is carefully situated in the context of a series of events going on London and alert us to what's happening (even if Mary is unconscious of how Henry is heading into danger, and Fanny too fails to read between the lines); and finally from the very beginning to the very end there are the touches of both cold disdainful mockery and genuine imaginative sympathy Mary is occasionally capable of.
The letters are as follows:
1) Letter from Mary, London, to Fanny, Portsmouth, telling of her first meeting with Mrs Rushworth and Julia (Mansfield ParkChapman III:9, 393-4; Penguin 40:386), in which Mary says she hopes Maria's access to splendor will satisfy her, mocks Yates as a sad catch for Julia ("if his rents were but equal to his rants"), and says she misses Edmund, Fanny, and so does Henry ("write me a pretty one in reply to gladden Henry's eye");
We are nowadays very alive to the debt modern novels which present a strongly persuasive psychologized consciousness as the central passages of the text owe to epistolary narrative. It has been shown more than once that Jane Austen learned to use narrative for clear revelation of a character's inmost self from the epistolary narratives that were so popular in her period, and that heavily influenced gothic novels, both of which she consumed (e.g., Margaret Lenta "Form and Content: A Study of the Epistolary Novel" UTC Studies in English, Vol 10, 1980, 14-30). We forget that epistolary narrative also tell stories, plots, and that by doing so in a disguised single- voice perspective they provide the novel with both suspense (the character who reads the letter doesn't get what's coming any more than the character who writes it) and dramatic irony (the reader is supposed to get it).
Austen is using letters to tell her story, to fit into Mansfield Park a subnovel or novel at a distance which we may glimpse the first time (in the way we catch on to a few of the clues in Emma), but which on the second reading we get much more of (in the way we read Emma so differently on the second reading).
The other element I want to add to Helen's posting is that we are expected to read Mary's letters alongside Edmund's, for the two sets gain meaning in terms of one another. Edmund writes two. Now his perspective on how Mary "welcomed" him is quite different from Mary's. Here we have the usual revelation of character and differing points of view modern readers are alerted to. but we should also note that as well as providing a counterpoint to Mary's letters, a backdrop (so to speak) in which we find Edmund gradually finding himself an alien in Mary's inner & outer worlds, Edmund too, obtuse as he is, tells us a little more about this story of Henry and Maria that is going on in London. The final letter written by him in which he too gives us the climax of Henry and Maria's story (as well as his and Mary's) is also meant to contrast to Mary's: it is deliberate & anguished. It also compares, for, like Mary, he is utterly self-involved and cannot see any point of view about the interview but his own; both are brief. The author however expects us to distance ourselves and judge impartially based on high standards of integrity and kindness Austen assumed her readers shared with her.
For those who would like to look at Edmund's letters and see how they are psychologically counterpointed to Mary's while filling in an objective story we are supposed to pick up from both their letters, here are pages:
1) Letter from Edmund, Mansfield, Park, to Fanny in Portsmouth (Mansfield Park Chapman III:13, 420-23; Penguin 44:411-414) in which Edmund actually details scenes from London including something of what happened on the important night of Mrs Frazer's party; and in which his real love for Fanny comes out because while he says Mary is "the only woman in the world whom I could ever think of for a wife" the woman he misses, longs for, cannot bear not to have at "home" with him is Fanny; and