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SYDNEY CHAPMAN, ESQ., D.SC, ON 



it tending to move it bodily. In early days the direction of the 

 axis was supposed to be truly north and south, but it is now 

 known that in most parts of the earth this is only approximately 

 the case. This directive property of magnets was probably 

 discovered independently among the Eastern and the Western 

 nations, becoming known in Europe about the twelfth century 

 of our era, and earlier still in China and Japan. 



This second discovery was of great practical importance and 

 was soon turned to use in navigation. The magnet points 

 sufficiently nearly to true north for it to be of great value to 

 mariners, since it provided a means, v/hich had hitherto been 

 wanting, of indicating direction when out of sight of land cr — 

 through cloudiness of sky — of the heavenly bodies. Thus the 

 ship's compass was invented, the early forms consisting of a 

 small needle-shaped magnet attached to a floating bowl or card, 

 on which, later on, the points of the compass began to be marked. 

 Many improvements in construction have been introduced in 

 the course of centuries, and the use of iron in the structure of 

 modern ships has necessitated the addition of special auxiliary 

 devices to compensate for the disturbing effects on the compass. 

 Fundamentally, however, the compass remains the same, and is 

 still one of the most important aids to seamanship — and, it is 

 becoming possible to say, of airmanship also. 



In time it was found that the peculiar properties of the natural 

 magnet could be communicated, by rubbing, to pieces of iron, 

 and that, if the iron was not too soft, the magnetization is re- 

 tained for a considerable period. It thus became possible to 

 prepare artificial magnets and compass needles. The first 

 European treatise on the magnet seems to have been written 

 in 1269 by Petrius Peregrinus, a Frenchman, and a disciple of 

 Roger Bacon. He made precise experiments on the magnetic 

 aura or sphere of influence surrounding a magnet, to which 

 its properties were generally referred ; in the language of modern 

 science, this is termed " a field of magnetic force,'' but without 

 any essential diflerence of meaning. Peregrinus thus clearly 

 describes how the direction of force at the surface of a magnet 

 can be mapped out and its poles determined : " The stone is 

 to be made in globular form and polished in the same wa\ as 

 are crystals and other stones. Thus it is caused to conform in 

 shape to the celestial sphere. Now place upon it a needle or elon- 

 gated piece of iron, and draw a line in the direction of the needle, 

 dividing the stone in two. Then put the needle in another 



