278 FRAGMENTS OF SCIENCE. 



effects which we have observed in our private chambers. 

 Why, we inquire, does the magnetic needle set north and 

 south? Evidently it is compelled to do so by the earth; 

 the great globe which we inherit is itself a magnet. Let us 

 learn a little more about it. By means of a bit of wax or 

 otherwise, attach the end of your silk fiber to the middle 

 point of your magnetic needle; the needle will thus be un- 

 interfered with by the paper loop, and will enjoy to some 

 extent a power of "dipping" its point, or its eye, below 

 the horizon. Lay your bar-magnet on a table, and hold 

 the needle over the equator of the magnet. The needle 

 sets horizontal. Move it toward the north end of the 

 magnet; the south end of the needle dips, the dip aug- 

 menting as you approach the north pole, over which the 

 needle, if free to move, will set itself exactly vertical. 

 Move it back to the center, it resumes its horizontality; 

 pass it on toward the south pole, its north end now dips, 

 and directly over the south pole the needle becomes vertical, 

 its north end being now turned downward. Thus we learn 

 that on the one side of the magnetic equator the north end 

 of the needle dips; on the other side the south end dips, 

 the dip varying from nothing to ninety degrees. If we go 

 to the equatorial regions of the earth with a suitably sus- 

 pended needle we shall find there the position of the needle 

 horizontal. If we sail north one end of the needle dips; if 

 we sail south the opposite end dips; and over the north or 

 south terrestrial magnetic pole the needle sets vertical. The 

 south magnetic pole has not yet been found, but Sir James 

 Ross discovered the north magnetic pole on June 1, 1831. 

 In this manner we establish a complete parallelism between 

 the action of the earth and that of an ordinary magnet. 



The terrestrial magnetic poles do not coincide with the 

 geographical ones; nor does the earth's magnetic equator 

 quite coincide with the geographical equator. The direc- 

 tion of the magnetic needle in London, which is called the 

 magnetic meridian, encloses an angle of 24 degrees with 

 the astronomical meridian, this angle being called the 

 Declination of the needle for London. The north pole of 

 the needle now lies to the west of the true meridian; the 

 declination is westerly. In the year 1G60, however, the 

 declination was nothing, while before that time it was 

 easterly. All this proves that the earth's magnetic con- 

 stituents are gradually changing their distribution. This 



