† photo-magnetographn.
Obsolete.
An instrument for recording fluctuations of the earth's magnetic field in which a mirror attached to a compass needle reflects a beam of light on to a revolving drum whose surface is covered with light-sensitive paper.
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magnetograph1847
photo-magnetograph1893
1893 R. S. Ball Story of Sun 228 Facts of magnetic perturbations taken from the photo-magnetographs of the United States Naval Observatory.
This entry has been updated (OED Third Edition, March 2006; most recently modified version published online June 2018).
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n.1893