'Magnetograph' definitions:

Definition of 'magnetograph'

From: WordNet
noun
A scientific instrument that registers magnetic variations (especially variations of the earth's magnetic field)

Definition of 'Magnetograph'

From: GCIDE
  • Magnetograph \Mag*net"o*graph\, n. [Magneto- + -graph.] (Physics) An automatic instrument for registering, by photography or otherwise, the states and variations of any of the terrestrial magnetic elements. [1913 Webster]