Magnetic field lines similarly describe the structure of magnetic fields in three dimensions. They are defined as follows.
Field lines converge where the magnetic force is strong , and spread out where it is weak.
The behavior of field lines in the Earth's magnetic field is very similar. For many years they were viewed as merely a way to visualize magnetic fields, and electrical engineers usually preferred other ways, mathematically more convenient. Not so in space, however, where magnetic field lines are fundamental to the way free electrons and ions move. Exploring further A small bar magnet, on gimbals that allow it to point in any direction in space, can be procured from its manufacturer, Cochranes of Oxford, Ltd., Leafield, Oxford OX8 5NT, England.