To make an intelligent introduction of the solution which is to be disclosed, it will be of advantage to set forth briefly some principles that are well recognized among navigators. Defining the sub-celestial place of any body in the firmament as the point of intersection with the surface of the earth of a straight line drawn from the celestial body to the center of the earth, it will be evident that the geographical position of the sub-celestial place is in a latitude equal to the declination of the celestial body and in a longitude equal to the hour-angle of the celestial body from the prime meridian, and that the celestial body is in the zenith of the sub-celestial place.
The Sumner Line of Geographical Position and the Compass Error Serviceably Deduced by Inspection
By G.W. Littlehales