CHAPTER 29. THE NAVIGATOR.
Not only is Flinders to be regarded as a discoverer whose researches completed the world's knowledge of the last extensive region of the habitable globe remaining in his time to be revealed; not only as one whose work was marked by an unrivalled exactitude and fineness of observation; but also as one who did very much to advance the science of navigation in directions calculated to make seafaring safer, more certain, with better means and methods at disposal. Malte-Brun declared, when he died, that "the geographical and nautical sciences have lost in the person of Flinders one of their most brilliant ornaments,"* and that criticism, coming from a foreign critic than whom there was no better informed savant in Europe, was no mere piece of obituary rhetoric. (* Annales des Voyages 23 268.)
In 1805 he wrote a paper on the Marine Barometer, based upon observations made during his Australian voyages. The instrument employed was one which had been used by Cook; Flinders always kept it in his cabin. He was the first to discover, and this essay was the first attempt to show, the connection between the rise and fall of the barometer and the direction of the wind. Careful observation showed him that where his facts were collected the mercury of the barometer rose some time before a change from landbreeze to seabreeze, and fell before the change from seabreeze to landbreeze. Consequently a change of wind might generally be predicted from the barometer. The importance of these observations was at once recognised by men connected with navigation. As the Edinburgh Review wrote, dealing with Flinders' paper when presented before the Royal Society on March 27th, 1806:* "It is very easy for us, speculating in our closet upon the theory of winds and their connection with the temperature, to talk of drawing a general inference on this subject with confidence. But when the philosopher chances to be a seaman on a very dangerous coast, it will be admitted that the strength of this confidence is put to a test somewhat more severe; and we find nevertheless that Captain Flinders staked the safety of his ship and the existence of himself and his crew on the truth of the above proposition." (* Edinburgh Review, January, 1807; Flinders' Paper, "Observations on the Marine Barometer," was published in the Philosophical Transactions of the Royal Society, Part 2 1806.) Nowadays, indeed, the principal use of a barometer to a navigator aboard ship is to enable him to anticipate changes of wind.
Not less important were his experiments and writings upon variations of the compass aboard ship. The fact that the needle of a compass showed deviations on being moved from one part of a ship to another had been observed by navigators in the eighteenth century, but Flinders was the first to experiment systematically to ascertain the cause and to invent a remedy.* (* For the history of the matter see Alexander Smith's Introduction to W. Scoresby's Journal of a Voyage to Australia for Magnetic Research, 1859.)
He observed not only that the direction of the needle varied according to the part of the ship where it was placed, but also that a change in the direction of the ship's head made a difference. Further, he found that in northern latitudes (in the English Channel, for instance) 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.* (* See the excellent chapter on "Compasses" in Volume 2 of the British Admiralty's Manual of Seamanship.) 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.