The magnetic lines of force don't exist , they are defined by scientists.

磁力线并不存在，它是由科学家所定义。

youdao

It has been suggested that birds can sense the magnetic lines of force stretching from the north to south magnetic poles of the earth, and so direct themselves.

有人认为，鸟类能觉察得出地球自北向南磁极的磁力线，因而能为自己导向。

youdao

The existence of electric current in the conductor(not closed)which is cut-ting the magnetic lines of force(B-lines) variably in the magnetic field is pointed out, and the acceleration is discussed.

指出了在磁场中做变速切割磁力线（线）运动的导体（不闭合）中有电流存在，讨论了其运动加速度。

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The magnetic field lines are like the two lanes of traffic on a busy road: close together, but pointing in opposite directions.

ECONOMIST: Hot stuff

The same thing happens with the magnetic field lines, which suddenly reconnect, resulting in a hole a few kilometres wide in the armour of the magnetosphere, through which plasma can spill.

ECONOMIST: Hot stuff

There seems to be no way that particles streaming past the earth along magnetic field lines can make a turn, move at right angles to those lines for a bit and end up inside the magnetosphere.

ECONOMIST: Hot stuff