THE DIP OF THE COMPASS NEEDLE. 2OQ 



Thus Peregrinus revealed the presence of the magnetic 

 field a discovery which lies at the very foundation of all 

 electrical development. We may look upon him as be- 

 ginning a cycle which ended five hundred and fifty years 

 later, when Oersted saw his needle turn and place itself 

 anew in the field of force surrounding, not a lodestone, 

 but a wire through which an electrical current was passing. 



In the middle of the sixteenth century this seed which 

 Peregrinus planted reached the end of its long period of 

 germination. Or, perhaps, there had come into the world 

 people capable of reading more from the pages of his man- 

 uscript, than was there in words. At all events, by direct 

 inspiration from his writing came the discovery of the dip 

 or inclination of the compass needle, and the still more 

 definite recognition of a magnetic field of force. How this 

 happened I have now to tell. 



In March, 1544, Dr. George Hartmann, a native of Eck- 

 holtsheim, and a mathematician and astromoner of emi- 

 nence, wrote to Duke Albert of Prussia an account of 

 magnetic discoveries made during the preceding year, 

 which he had already explained to King Ferdinand of 

 Bohemia. He says : 



"In the second place I find also this in the magnet: 

 that not only does it decline from the north, and turn to 

 the east for nine degrees more or less as I have said, but it 

 also shows a downward inclination which may be demon- 

 strated as follows: Take a compass needle about the length 

 of a finger and place it on a point in a position exactly 

 horizontal (or on the water-level) so that neither end in- 

 clines to the earth and both sides are in exact equilibrium. 

 Now, if I rub either end of the needle once with a magnet, 

 the needle does not stand any longer balanced, but inclines 

 downwardly about nine degrees more or less. I have not 

 been able to demonstrate to his Majesty the cause of this 

 phenomenon." This was the first announcement, after 

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