316 POPULAR LECTURES AND ADDRESSES. 



force there is such as to pull the red end or pole 

 of a magnetized needle downwards, and to repel 

 the blue end upwards. It also has the effect of 

 inducing magnetism in any mass of iron, so as to 

 give it a transient magnetic quality marked with 

 blue on the upper side or end and red on the lower 

 side or end. Thus, in the northern magnetic 

 hemisphere the Flinders bar is transiently mag- 

 netized by the earth's vertical force in such manner 

 that it acts like a great bar-magnet with its upper 

 end blue and its lower end red. At the magnetic 

 equator it loses its magnetism, and in the southern 

 magnetic hemisphere it acquires magnetism in the 

 opposite direction to that which it had in the 

 northern hemisphere ; so that now its upper end is 

 red and its lower end blue. As the ship moves 

 from one hemisphere across the magnetic equator 

 to the other, the magnetism of the Flinders bar 



north of the equator is in the Indian Ocean, which it crosses from 

 Africa, a little south of Cape Guardafui, to the south of India, very 

 nearly along the 10 parallel of north latitude and eastward across 

 the mouth of the Bay of Bengal to the Malay Peninsula, still but 

 little short of this degree of north latitude. A chart of lines of 

 equal magnetic dip, such as the very convenient small scale one 

 of the Admiralty Compass Manual, should be carefully studied. 



