This is a practical pun:—You desire any one to stand on a chair or
table, and you tell him that, notwithstanding his weight, you will
bring him down upon a feather. You then leave the room, and procuring
a feather from a feather-bed, you give it to him, and tell him you
have performed your promise,—that you engaged to bring him _down_ upon
a feather, which you have done; for there is the feather, and, if he
looks, he’ll find _down_ upon it.