Of the numerous errors that may be classed under the general term of compass defaults, we may mention defective compasses arising from imperfect workmanship, or from an ignorance of the principles of mechanical and magnetical science, compasses perfectly adjusted but placed injudiciously either with reference to the magnetism of the ship, or in immediate proximity to concealed and unsuspected portions of iron. Ignorance of the degree of compass error arising from the ship's magnetism, and of its varying amount in changes of geographic position, and a consequent belief, that in all places and under all circumstances the needle is true to the north, are frequent causes of shipwreck. With regard to the defective mechanical construction of compasses, it must be admitted that great improvements have taken place of late years, and the chief credit, we believe, is due to the British Admiralty. Nearly twenty years ago they instituted a Committee of Inquiry, and the silent working of the measures then advocated, and the adoption of the improvements suggested first under the direction of the late Captain Johnston, and more recently under that of Mr. Frederick Evans, R.N., have infused into the manufacturers, and a large portion of the mercantile marine and shipowners, a degree of caution, skill, and attention to details, which has brought forth good fruit. A large portion of the superior compasses of the United States navy are manufactured in this country, entirely on the Admiralty pattern, and several foreign governments have recently obtained the same instruments as models. It must not however be supposed that defective compasses have ceased to exist. Our coasting vessels and many of our noble sailing ships are miserably equipped, and there are many captains who still look on the compass as a cheap and common article, fit to be classed with hooks and thimbles and other articles of the boatswain's storeroom. There can be no doubt that great errors in navigation are induced by inattention to placing the compasses. It is common to see the binnacle within two feet, and even less, of the massive iron-work of the rudder wheel, which again is in immediate contiguity with an iron sternpost. The local deviation is consequently great, magnet adjustment is had recourse to, and a temporary alleviation of the evil follows, which is only magnified on the ship approaching some distant port. Numerous examples are on record of iron being introduced by some addition to the equipment of the ship, which has perhaps been lost in consequence within a few hours after quitting port.