Scientific Lectures. 143 



SCIENTIFIC LECTITRE-III. 



MAGNETISM: THE EAETH A GKEAT MAGNET. 



By Professor A. M. Mayer, 



Of the Stevens Institute of Technology. Dec. 21, 1871. 



At the invitation of the Trustees of the American Institute, I have 

 the honor to appear before you to deliver a lecture on Magnetism, a 

 subject to which I have given several years of devoted study. 



Confused by the multiplicity of the facts of this science, and 

 embarrassed by the grandeur of its generalizations, I have resolved to 

 do, what every public lecturer must do, who would confer on his hearers 

 any greater benefit than mere temporary amusement, and that is, to 

 select from this subject one prominent truth, and to present this to 

 you in simple and striking experiments ; but, so to describe and logi- 

 cally connect these experiments as clearly and forcibly to bring the 

 truth before your minds and fix it there. 



That this method of procedure is necessary, will be evident when 

 you consider that over 100 men of the highest ability, as original 

 investigators, have toiled, on an average of ten years each, at these 

 problems of magnetism, thus making an aggregate of 1,000 years of 

 successful search in the rich mine of natural truth. 



From this vast accumulation of fact and of theory I select, as my 

 text, words given to the world over 270 years ago, by Dr. William 

 Gilbert, the physician to Queen Elizabeth. In the year 1600 Gilbert 

 published a work entitled " De Magnete," or, " On the Magnet.* In 



* Humboldt's Cosmos, volume 5, page 57: "About the close of the sixteenth century, William 

 Gilbert, a man who excited the admiration of Galileo [who said of him, 'great to a degree that 

 might be envied. 1 Cosmos, vol. 1, p, 170], although his merits were wholly unappreciated by Bacon, 

 first laid down comprehensive views of the magnetic force of the earth. * * * Like other men 

 of genius, he had made many happy results from feeble analogies, and the clear views which he had 

 taken of terrestrial magnetism {de magno magnete tellure), led him to ascribe the magnetism of the 

 vertical iron rods on the steeples of old church towers to the effect of this force. He, too, was the 

 first in Europe who showed that iron might be rendered magnetic by being touched with a magnet, 

 although the Chinese had been aware of the fact nearly 500 years before him. Even then Gilbert 



