天体が東西圏上を通過する時刻に関する一考察(日本航海学会第8回講演会)

抄録

In taking sight when the celestial bodies are on the prime vertical, we can get a exact Longitude at this time and observed noon position most quickly in the conbination with "Sighting" of noon. For above reasons, we are often endevouring to take advantage of an opportunity to take sight at that time. So, I drew the graph, by which we can get "Hour Angle on the Prime Vertical" very easily and exactly and determine previously the time to take sight.