If sooty bubbles form and blacken on the wick in a lamp burning whale oil, each bubble indicates the receipt of a letter.
Peabody, Mass.

If sooty bubbles form and blacken on the wick in a lamp burning whale oil, each bubble indicates the receipt of a letter.
Source: Current Superstitions (1896), entry 1458.
Fanny D. Bergen, editor.
Modern normalized navigation; the historical attribution above remains unchanged.