It is essential not only that the wind should move with great velocity and steadiness to supply a sufficiently copious and continuous stream of snow-dust, but that it should come from the north.

重要的是，风不仅要以极快的速度和稳定的速度移动， 以提供足够丰富和连续的雪尘流， 而且风应该来自北方。

It is essential, therefore, not only that the wind should move with great velocity and steadiness to supply a sufficiently copious and continuous stream of snow-dust, but that it should come from the north.

因此，至关重要的是， 风不仅要以极快的速度和稳定的速度移动， 以提供足够丰富和连续的雪尘流， 而且还应该来自北方。