Isoclinal lines

from The Collaborative International Dictionary of English v.0.48

Isoclinal \I`so*cli"nal\, Isoclinic \I`so*clin"ic\, a. [Iso- +
   Gr. ? to incline.]
   Of or pertaining to, or indicating, equality of inclination
   or dip; having equal inclination or dip.
   [1913 Webster]

   {Isoclinal lines} (Magnetism), lines on the earth's surface
      connecting places at which a dipping needle indicates the
      same inclination or dip.
      [1913 Webster]