258 NOETH MAGNETIC POLE AND NORTHWEST PASSAGE. 



different on every point of tlie surface of the earth, nor is it always 

 the same in one and the same place. It is subject to regular daily 

 and yearl}^ changes, and, similarly, there often occur irregular, more 

 or less violent, disturbances. Finally, small displacements show them- 

 selves from year to year, which continue in the same manner for a 

 long series of years. All this has been discovered through observa- 

 tions undertaken during the course of time at various parts of the 

 surface of the globe, partly during travels and partly by permanent 

 stations. A careful study of all the available material which had 

 been acquired by observation caused the great German mathematician 

 and physicist. Gauss, in the thirties of last century, to form a theory 

 as to the sequence and varied appearance of the phenomena of terres- 

 trial magnetism at a certain moment of time according to the geo- 

 graphical latitude and longitude. It thus became possible to con- 

 struct three different maps, of which two show the direction of the 

 force and the third its strength. The reason why two maps are 

 necessar}^ for direction is because the direction must be given both 

 in relation to the north and to the south geographical line, and in 

 proportion to the horizontal plane of a place. The direction of the 

 terrestrial magnetic force in relation to the north-to-south line can 

 be observed b}^ the help of the compass, which, as we know, generally 

 points somewhat east or west of this same north. This divergence 

 is called the variation or the declination. On a magnetic map lines 

 are drawn which show the direction of the magnetic needle at every 

 point of the earth's surface. These lines, which are called magnetic 

 meridians, converge at two points — the north magiietic pole on the 

 Arctic coast of North America, and the south magnetic pole in the 

 interior of the Antarctic Continent. Each of the lines indicates, as 

 Avill be understood, the direction one would go if he followed exactly 

 the direction indicated by the north or south end of the magnetic 

 needle. In the first case, one would at length arrive at the north 

 magnetic pole ; in the other, at the south magnetic pole. 



If a magnetic needle be placed so that it can turn on an axis 

 through its center of gravity — exactly like a grindstone — the needle 

 will of itself adopt a diagonal position when the plane of revolution 

 is identical with the direction which the needle of a compass indi- 

 cates. An instrument of the kind is called an " inclinatorium," and 

 the angle which the dipping needle forms with the horizontal plane is 

 called the magnetic inclination of a place. Here, in our parts, the 

 north end of the needle points down toward the earth ; in Australia, 

 on the contrary, it is the southern end which dips. At the north 

 magnetic pole the dipping needle assumes a vertical position with 

 its north end down ; at the south magnetic pole it assumes a vertical 

 position with its south end down. The inclination, then, at both 

 their points is 90°, and decreases according as the distance becomes 



