TERRESTRIAL MAGNETISM, ETC. 241 



article. In the meantime, any reader who is 

 sufficiently interested may experiment for himself 

 upon the mutual influence between the bar-magnet 

 and the floating needle, and between two needles 

 separately magnetized and floated. He may even 

 readily enough anticipate Gilbert's discovery, and 

 particularly his reasons for marking the poles N 

 and S in the manner illustrated in the preceding 

 sketch, which is at variance with the rule un- 

 happily still followed by British instrument-makers, 

 notwithstanding Gilbert's strong and early re- 

 monstrance against it 



The first part of this article was written five 

 years ago. I then thought I had a pleasant and 

 easy task before me in the completion of it to 

 describe a scientific instrument which was known 

 to the Chinese two thousand years before the dawn 

 of science, and first used by them as a guide across 

 the deserts of North-Eastern Asia ; which for six 

 hundred years has been in regular use by European 

 mariners as a guide at sea ; and which is now of 

 ancient and world-wide renown as an appropriation 

 from the most recondite province of modern 

 VOL. in. R 



