Isodynamic lines

from The Collaborative International Dictionary of English v.0.48

Isodynamic \I`so*dy*nam"ic\, a. [Iso- + dynamic.]
   Of, pertaining to, having, or denoting, equality of force.
   [1913 Webster]

   {Isodynamic foods} (Physiol.), those foods that produce a
      similar amount of heat.

   {Isodynamic lines} (Magnetism), lines on the earth's surface
      connecting places at which the magnetic intensity is the
      same.
      [1913 Webster]