A man sits at the office after drinking far too much wine, and when he looks at his hat, it seems to him like money lying in the street. That's the whole scene, and its humor comes from how small and oddly specific it is. The speaker's drunken eyes turn an ordinary object into a surprise, the kind of lucky find that makes you stop and stare.
The comparison works because of what it quietly suggests. A hat is something you own, yet here it feels like a windfall, as if he has to rediscover his own belongings. The title, "Apparition," treats the hat almost like a ghost appearing out of nowhere. Judging by the tone, the speaker feels amused and a little dazed, perhaps pleased with himself. There's also a faint mischief in drinking at work, where he should be sober. The mood is light, wry, and dreamy, a brief flash of wonder found in the middle of a dull setting.