What is the origin of the idiom "comparing apples and oranges," as in,
You can't compare those things! That's like comparing apples and oranges.
EDIT: I can find a book from 1889 making the comparison.
Update: 30/03/2017
It appears that the link cited above is broken.
Best Answer
The American Heritage Dictionary of Idioms (1997) offers this derivation of "apples and oranges":
In Ray's book, it appears in the section called "Proverbial Similes" and consists of the simple phrase "As like as an apple to an oyster."
The Wordsworth Dictionary of Proverbs (2006) offers this series of early quotations: