Notice of Dr. Scoresbyh Magnetical Investigations. 33 



Art. III. — Magnetical Investigations; by the Rev. William 

 ScoRESBY, B. D. — Part I. London, Longman & Co., 1839. 

 pp. 96. — Part IL London, Longman & Co., 1843. pp. 360. 



The knowledge of the attractive property of the native mag- 

 net is of remote antiquity, and the possibihty of communicating 

 that virtue to iron and steel was perhaps ascertained at a date lit- 

 tle less distant. The direction property, of such absolute neces- 

 sity to the navigator, and so convenient to the land surveyor, was 

 certainly unknown to the polished nations of ancient Europe, 

 but there is reason to suppose that the Chinese, even before the 

 Christian era, were acquainted with it, and used it to guide the 

 courses of caravans upon the land, and of their junks upon the 

 ocean. The use of the needle for the latter purpose, among the 

 western nations of the old continent, is supposed to have been 

 introduced by the navigators of Atnalfi in Italy, although of this 

 there is no positive evidence ; but the instrument did not inspire 

 unlimited confidence in the certainty of its indications until the 

 15th century, when a career of maritime discovery was opened 

 under its influence, which had its proudest triumph in the first 

 voyage of Columbus. 



In that eventful expedition, the fact that the needle did not 

 every where point to the poles of the earth, was first detected, 

 and from that time to the present, the variation of the compass 

 has been a subject of close and assiduous study, first as essential 

 for the safety of the navigator, and finally as an important ele- 

 ment in the magnetic properties of the earth itself. The simple 

 fact of the existence of the dip could not have escaped any art- 

 ist who had constructed a compass, but it was not until the mid- 

 dle of the last century, that the dipping needle came to be con- 

 sidered as an essential part of magnetic apparatus, although used 

 by Norman in A. D. 1592. 



The probability that the intensity of the magnetic influence 

 varied in diflerent parts of the earth's surface, seems to have been 

 first distinctly pointed out, in the instructions for the voyage of 

 La Perouse, but it was reserved for Humboldt to establish the 

 certainty of this variation in the force, by experiment. 



It was also known that these three elements, direction, inten- 

 sity and dip, were not constant at any given place, and the dis- 



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