The first class of readers may be compared to an hour-glass, their reading being as the sand; it runs in and runs out, and leaves not a vestige behind. A second class resembles a sponge, which imbibes everything, and returns it in nearly the same state, only a little dirtier. A third class is like a jelly-bag, which allows all that is pure to pass away, and retains only the refuse and dregs. The fourth class may be compared to the slave of Golconda, who, casting aside all that is worthless, preserves only the pure gems.