Gloaming, means ‘twilight’ or ‘dusk’ and comes from the Old English word glōmung. Scott also comments on the variability of the wind and the difficulty of ‘sailing’:
The wind is strong from the south, and this afternoon has been very helpful with the full sail.
But soon after;
Blizzards are our bugbear, not only stopping our marches but the cold damp air takes it out of us.