The angle between the point at which the sun rises and sets, and the true east and west points of the horizon. Amplitudes were used historically to find the error of the magnetic compass in order to establish the variation, the difference of either the morning or evening amplitude from the mean being the correction required. This was first suggested by Francisco Faleiro in his Tratado del sphera y del arte del marear (1535). In 1595 the mathematician Thomas Hariot produced the first table of amplitudes for use at sea which was published in the introduction to the Instructions for Ralegh's Voyage to Guinea.
Subjects: Maritime History.