Rapid oscillations of the barometer should never be interpreted as presaging dry or rainy weather of any duration.

Those indications are given exclusively by the rising or the falling which takes place in a slow and continuous manner.
7.

Toward the end of autumn, if after prolonged rainy and windy weather, the barometer begins to rise, that rising announces the passage of the wind to the north and the approach of the frost.
Such are the general consequences to draw from the indications of this precious instrument.
Dick Sand knew all that perfectly well, as he had ascertained for himself in different circumstances of his sailor's life, which made him very skilful in putting himself on his guard against all contingencies.
Now, just toward the 20th of February, the oscillations of the barometrical column began to preoccupy the young novice, who noted them several times a day with much care.

In fact, the barometer began to fall in a slow and continuous manner, which presages rain; but, this rain being delayed, Dick Sand concluded from that, that the bad weather would last.

That is what must happen.
But the rain was the wind, and in fact, at that date, the breeze freshened so much that the air was displaced with a velocity of sixty feet a second, say thirty-one miles an hour.
Dick Sand was obliged to take some precautions so as not to risk the "Pilgrim's" masting and sails.
Already he had the royal, the fore-staff, and the flying-jib taken in, and he resolved to do the same with the top-sail, then take in two reefs in the top-sail.
This last operation must present certain difficulties with a crew of little experience.