A HISTORY OF SCIENCE 



magnetic attraction of the earth, and to predict where 

 the vertical dip would be found. These deductions 

 seem the more wonderful because at the time he made 

 them the dip had just been discovered, and had not 

 been studied except at London. His theory of the 

 dip was, therefore, a scientific prediction, based on a 

 preconceived hypothesis. Gilbert found the dip to 

 be 72 at London; eight years later Hudson found the 

 dip at 75 22' north latitude to be 89 30' ; but it was 

 not until over two hundred years later, in 1831, that 

 the vertical dip was first observed by Sir James Ross 

 at about 70 5' north latitude, and 96 43' west 

 longitude. This was not the exact point assumed 

 by Gilbert, and his scientific predictions, therefore, 

 were not quite correct; but such comparatively slight 

 and excusable errors mar but little the excellence of 

 his work as a whole. 



A brief epitome of some of his other important dis- 

 coveries suffices to show that the exalted position in 

 science accorded him by contemporaries, as well as 

 succeeding generations of scientists, was well merited. 

 He was first to distinguish between magnetism and 

 electricity, giving the latter its name. He discov- 

 ered also the "electrical charge," and pointed the way 

 co the discovery of insulation by showing that the 

 charge could be retained some time in the excited 

 body by covering it with some non-conducting sub- 

 stance, such as silk ; although, of course, electrical con- 

 duction can hardly be said to have been more than 

 vaguely surmised, if understood at all by him. The 

 first electrical instrument ever made, and known as 

 such, was invented by him, as was also the first mag- 



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