THE FIRST MEASUREMENT OF DIP. 215 



man puts it, "that if the compasse or needle shew not the 

 pole, the fault is in placing the wiers on the flie, and not 

 in any propertie it hath to vary." 



All of these earlier theorists he thinks went "farre wide 

 from the Attractive point," and the reason they did so is 

 their ignorance of a "certaine Declining propertie under 

 the Horizon, lately found in the needle." This is his dis- 

 covery, which he describes in the following terms : "Hav- 

 ing made many and divers compasses, and using alwaies 

 to finish and end them before I touched the needle, I found 

 continually that after I had touched the yrons with the 

 Stone, that presently the north point thereof would bend 

 or Decline downwards under the Horizon in some quan- 

 titie ; insomuch that to the Flie of the Compasse which 

 before was made equall, I was still constrained to put some 

 small peece of waxe in the South part thereof, to counter- 

 poise this declining, and to make it equall againe." He 

 noticed this repeatedly without deeming the occurrence 

 of any moment, until some one employed him to make an 

 instrument in which the needle was to be five inches long. 

 He constructed the apparatus with his usual care, balanced 

 the needle with the utmost nicety, and then magnetized 

 it ; whereupon the north end dipped. Not wishing to add 

 wax, he sought to restore the balance by cutting off some 

 of the inclining end ; but he removed too much, and 

 spoiled his work. Although, as he says, "thereby beeing 

 stroken in some choller," he at once determined to find 

 out the cause of this inclining, and thereupon he sup- 

 ported a needle on a horizontal pivot, so that it could 

 move freely around a vertical circle, which he graduated 

 in quadrants after the fashion of the Astrolabe. Then, for 

 the first time, it became possible to measure the whole 

 angle of inclination or dip of the needle below the horizon, 

 and Norman records it as about 71 50'. l 



How was this to be accounted for? Not by any acces- 



was in 1576. The angle afterwards increased to 74 42' in 1720, 

 since which time it has been decreasing. 



