In an example of dramatic irony, readers are aware of the fact that Mr. Featherstone died with two wills, but most of the people of Middlemarch are not. While Mr. Featherstone’s family—particularly Fred—become excited at the reading of the first will because it divides Mr. Featherstone’s wealth up amongst known family members, they are shocked to learn of a second will and are alarmed by its contents (since all of his money goes to the unknown entity Mr. Rigg), as seen in the following passage:
And at the sound of the first "give and bequeath" she could see all complexions changing subtly, as if some faint vibration were passing through them, save that of Mr. Rigg. He sat in unaltered calm, and, in fact, the company, preoccupied with more important problems, and with the complication of listening to bequests which might or might not be revoked, had ceased to think of him. Fred blushed, and Mr. Vincy found it impossible to do without his snuff-box in his hand, though he kept it closed.
The descriptions that, as they learned about the money going to Mr. Rigg, Mr. Featherstone’s family’s “complexions chang[ed] subtly”—with Fred blushing and Mr. Vincy anxiously playing with his snuff-box—show that they were shocked by this ironic change of events.
In addition to dramatic irony, the fact that the second will states Mr. Featherstone’s money will go to a son he had from a secret relationship is also an example of situational irony—Fred has been banking on receiving that money in order to get himself out of debt and everyone in town assumed he would receive it.
Dorothea falling in love with and marrying Will is an example of situational irony because she has been explicitly forbidden from marrying him by her late husband Casaubon (who was deeply jealous of his younger cousin Will). Part of the irony is that Dorothea did not even consider marrying Will until Causabon’s will forbade it, as seen in the following passage:
Then again she was conscious of another change which also made her tremulous; it was a sudden strange yearning of heart towards Will Ladislaw. It had never before entered her mind that he could, under any circumstances, be her lover: conceive the effect of the sudden revelation that another had thought of him in that light—that perhaps he himself had been conscious of such a possibility,—and this with the hurrying, crowding vision of unfitting conditions, and questions not soon to be solved.
As the narrator makes clear, “it had never before entered [Dorothea’s] mind” that Will could be a romantic partner for her—it was only because Casaubon suggested it that it has now entered her mind. Here Casaubon’s greed and desire to control Dorothea backfire.
There is also a more subtle layer of dramatic irony at play in that readers have been able to sense over the course of the novel that Dorothea has been in love with Will, so her "big" revelation that she has been in love with him since Rome is not entirely surprising.
