I glanced at the instrument, which, together with a tell-tale compass, swung from the skylight transoms, and saw that the mercury had sunk in the tube to the extent of nearly an inch since the last setting of the vernier; and, as it was our custom in the Slave Squadron at that time to set the instrument at 8 o'clock a.m. and 8 o'clock p.m., it meant that the mercury had fallen to that extent during the night!
