Page:The life of Matthew Flinders.djvu/529

 ) the north end of the needle was attracted towards the bow of the ship; whilst in southern latitudes, in Bass Strait, there was an attraction towards the stern; and at the equator there was no deviation. He came to the conclusion that these results were due to the presence of iron in the ship. When he returned to England in 1810, he wrote a memorandum on the subject to the Admiralty, and requested that experiments might be made upon ships of the Navy, with the object of verifying a law which he had deduced from a long series of observations. His conclusion was that "the magnetism of the earth and the attraction forward in the ship must act upon the needle in the nature of a compound force, and that errors produced by the attraction should be proportionate to the sines of the angles between the ship's head and the magnetic meridian." Experiments were made at Sheerness, Portsmouth, and Plymouth on five vessels. He took a keen personal interest in them; and the result was his invention of the Flinders' bar, which is now used in every properly equipped ship in the world. The purpose of the bar, which is a vertical rod of soft iron, placed so that its upper end is level with or slightly above the compass needle, is to compensate for the effect of the vertical soft iron in the ship. Flinders' work upon this technical subject was important even in the days of wooden ships. In this era of iron and steel ships it is regarded by every sailor as of the utmost value.

In Flinders' day the delicacy of the compass, its liability to error, the nature of the magnetic force to which it responds, and the necessity for care in its handling, were very little appreciated. "Among the nautical instruments taken to sea there are not any so