MAGNETISM. 



425 



What is a Dip- 

 ping Xeedle ? 



may roll or lurch, the card is al- FiG 355. 



ways in a horizontal position, 



and is certain to point the true 



direction of the head of the ship. 



Fig. 355 represents the construc« 



tion and mounting of the Sea 



Compass. 



797. If a 

 simple bar 



of unmagnetized steel, 

 or an ordinary needle 

 be suspended from a 

 center, instead of being balanced upon a pivot beneath 

 it, it will bang horizontally, and manifest no inclination 

 to dip from a horizontal line, either 

 on one side or the other of the cen- 

 ter of suspension. But if the bar, 

 or needle, be made a magnet, it 

 will no longer lie in a horizontal 

 direction, but one pole will incline 

 downward and the other upward ; 

 the inclination in this latitude to 

 the horizon being about 70°. 



Such arrangement is called 

 Dipping Needle. 



Fig. 356. represents the construction and 

 appearance of the dipping needle. 



798. Although the 

 magnetic needle is said 

 to point north and south, accurate observations 



have shown that it does not point exactly north and south 

 except in a few restricted positions upon the earth's surface. 

 What is the 799. The direction assumed by a horizontal 



magnsUc mend- n « 



unf needle m any given place upon the earth's 



surface, is called the magnetic meridian, 



A terrestrial meridian, it will be remembered, is a great cir- 

 cle, supposed to be drawn around the earth, passing through 

 both poles, and any given place upon its surface, and inter- 

 Becting the equator at right angles. (See § 68, Fig. 6, page 36.) The direction 



Does the mag- 

 netic needle 

 point due north 

 and south. 



What is a ter- 

 restrial merid- 

 ian? 



