Page:Polar Exploration - Bruce - 1911.djvu/223

Rh neighbourhood of the South Magnetic Pole, as well as those of Bernacchi, are of the highest possible value. Further observations in circles round about the approximate point of each magnetic pole would add very much to our knowledge of terrestrial magnetism.

Terrestrial magnetism is altogether a most intricate and difficult science, but it is perfectly obvious that one very great use of an intimate study of this subject is for purposes of navigation. In the days of sailing ships, the finest course that was laid till recent years was to a quarter of a point or nearly three degrees of the circle, nowadays no steamer of any importance steers a wider course than one degree. The Mauretania, for instance, Captain W. T. Turner tells me, "is steered and the course set to degrees." In one instance, at least, I know of the captain of one liner insisting on an accuracy of a quarter of a degree, the helmsman keeping the course to that amount of accuracy by means of a magnifying glass placed over the compass card. With fine courses, such as those that are necessary for the high speeds attained, with the great value of these modern leviathans, with valuable cargoes, and with a thousand or more human beings on board, it will be seen how important an accurate knowledge of terrestrial magnetism is.