Is tone the attitude conveyed by the audience who reads the essay?

Close, but flip the perspective: when you're talking about elements of literature, "tone" is the attitude conveyed by the author (by the speaker or the writer, and not by the listener or the reader). So in this case, you'd need to say that "tone is the attitude conveyed by the author of the essay."

Whether it's a person giving a speech, a poet writing a poem, a blogger writing a post, or a novelist writing...

Close, but flip the perspective: when you're talking about elements of literature, "tone" is the attitude conveyed by the author (by the speaker or the writer, and not by the listener or the reader). So in this case, you'd need to say that "tone is the attitude conveyed by the author of the essay."

Whether it's a person giving a speech, a poet writing a poem, a blogger writing a post, or a novelist writing a book, it's the creator of the words who establishes the tone (and not the person who hears or reads the words).

That's why we say things like "the author's tone," "the essay's tone," "the poet's tone," "the poem's tone," and so on.

You might define "tone" more fully by saying it's the attitude that the writer expresses toward whatever subject he or she is writing about, or the attitude expressed toward whoever the writer is talking to.

Let's say you're writing a thank-you note. You say, "Dear Grandma, I want to thank you for the check you sent me for my birthday. It's really sweet of you to think of me and be so generous! I'm planning to put some of it in my savings account, and use the rest right now to get a new outfit for school. I'll think of you when I wear it. Love, your grandson."

In your note, you're the author, and your tone is one of gratitude, kindness, and warmth. You reveal your tone through your choice of words.

Further, your tone is directed toward your subject matter (the birthday check and the new outfit) and toward the person you're addressing (Grandma).

Let's take a more literary example. In Longfellow's poem "A Psalm of Life," he says things like "Act,— act in the living Present!" and "Let us, then, be up and doing." Longfellow is the writer of the poem, and he uses his word choice to establish a tone of encouragement, warmth, and excitement. His tone is aimed at his subject matter: the need to live life to the fullest.