Readers of Captain Cotter's paper under this title in the April 1976 issue of the Journal may be interested in some evidence that Dutch seamen in the seventeenth century were aware of this phenomenon of ship magnetism.

Abraham de Graaf in De seven Boecken van de Groote Zeevaert, published at Amsterdam in 1658, warns ships' officers taking bearings with the compass-that metal objects in their clothing can seriously deflect the compass, and mentions iron buttons and buckles. This was an important contemporary work on navigation and de Graaf was an examiner of officers of the Dutch East Indies Company from 1679 to 1714.