In other words, a compass needle will point straight down all along the circumference of the polar opening giving, as with the false geographic North Pole, a circle of magnetic North Poles, as the lines of force traverse the interior of the Earth.
(a compass needle; will point; L:straight down all along the circumference of the polar opening) (the lines of force; traverse; the interior of the Earth)
a compass needle the lines of force
will point traverse
L:straight down all along the circumference of the polar opening
the interior of the Earth