How do you properly add external magnets?

[mikebalcos]

I'm considering to add external magnets to my Athearn F7A's motor. This engine was bought in the 90's and I think it's American made. So how do you properly add the magnets? Should they attract to the magnet inside by positioning the opposite poles, or repel by positioning like poles?

 

[Russ Bellinis]

I think you want the magnets to attract so that the added magnets strengthen the magnetic field.