THE MARINER'S COMPASS.

New Zealand Herald, Volume XLVIII, Issue 14692, 29 May 1911, Page 8

THE MARINER'S COMPASS.

VARIATIONS IN MANY SEAS.

WORK OF CARNEGIE INSTITUTE. [BT TELEGRAPH. —OWN CORRESPONDENT.] Wellington, Sunday. A distinguished visitor to Wellington is Dr. Lewis Bauer, one of tlio world's most eminent authorities on terrestrial magnetism and director of the Dejvartment of Terrestrial Magnetism in ho Carnegie Institute, Washington. That institution has sent him out to plough the five seas with the Carnegie, a vessel specially designed for magnetic observations.

It has been known for some time, said Dr. Bauer yesterday, that the compass needle does not point true to the pole, but makes an angle into the true north and south line. This angle not only varies from place to place as one travels over the earth, but also changes its anglo during the course of a day. During foggy or cloudy weather, when tho sun or stars cannot be seen, the mariner must depend solely on the compass and the log for the navigation of his vessel. Hence it. is necessary for him to have an accurate chart of the so-called lines of equal magnetic variation, to enable him to quickly t-elj how far the compass points away from tho true north or south. During the cruiso of tho Carnegie in the Atlantic Ocean, between Brooklyn and Capetown, tho errors found in tho present compass charts amounted at times to as much as three degrees, and the errors unfortunately ran systematically in the fame direction for stretches of several thousand miles. However, tho charts are now being reconstructed with all possible despatch.

Dr. Bauer says that the purpose of tho present survey is not only to obtain tho necessary data for the perfection of ocean charts (for the present), hut also to derivo the necessary corrections to bring all data up to date. The department is engaged not only in obtaining the compass directions at various places throughout the world, but also tho changes recurring annually. This is done by reoccupying stations where previous observations were made at intervals of about five years. The Carnegie's predecessor, the Galilee, was in New Zealand waters at the end of 1906. At present the Carnegie is at Colombo under the charge of Dr. Bauer's assistant (Mr. E. Kitson), formerly attached to the Christchurch magnetic observatory. The chief expects to meet his lieutenant cat Colombo. When the Galileo finished her cruisu laborious corrections had to be made becauso tho vessel's iron and steel parts had vitiated the readings of the delicate magnetic instruments. Dr. Bauer has taken no risk with the Carnegie. She is a sailer with an ingenious auxiliary gas engine, of which the only iron parts are the pistons and cams. These are the only magnetic materials in the ship, and they arc too far away from the instruments to have any appreciable effect. The four anchors, weighing altogether 55001b, are of manganese bronze, which does not influence the instruments. Some llin hawsers take the place of anchor chains. Theso elaborate precautions enable the expedition to rapidly publish the results of the observations.