Take a glass rummer that is narrow at bottom and wide at top, into
which put a half-sovereign, and fill the glass three-fourths with
water; place on it a piece of paper, and then a plate, and turn the
glass upside down quickly, that the water may not escape: by looking
sideways at the glass, you will perceive a sovereign at the bottom, and
higher up the half-sovereign, floating near the surface. Fill the glass
with water, and the large piece only will be visible.