164 MAGNETICAL EXPERIMENTS, 



one of its poles towards the horizon, and of elevating the 

 other pole above it. This property was discovered in the 

 year 1576, It is found to be always the same at the same 

 place, but different in different places. 



Questions. — 1. When was the polarity of the magnet discovered? 

 2. What use was made of this property of the magnet ? 3. When and 

 by whom was the deviation of the needle from the meridian discovered ? 

 4. What is said of this variation with respect to the same place ? — to 

 different places ? 5. What is said of the declination of the needle at 

 London? 6. What is the inclination or dipping of the magnetic 

 needle ? 



LESSON 73. 



Magnetical ExpenHmcnts. 



The natural magnet, or loadstone, is found in the earth, 

 generally in iron mines, in a hard and brittle state, and for 

 the most part, more vigorous in proportion to the degree of 

 hardness. Artificial magnets, which must be made of hard 

 or highly tempered steel, are now generally used in prefer- 

 ence to the natural magnet ; not only, as they may be pro- 

 cured with greater ease, but because they are far superior to 

 the natural magnet in strength, communicate the magnetic 

 virtue more powerfully, and may be varied in their form 

 more easily. In making artificial magnets, care should be 

 taken to apply the north pole of the natural magnet or mag- 

 nets to that extremity of the steel which is required to be 

 made the south pole, and to apply the south pole of the mag- 

 net to the opposite extremity of the piece of steel. Very 

 powerful magnets may be formed by first constructing several 

 weak magnets, and then joining them together to form a 

 compound one. 



The north or south poles of two magnets repel each other ; 

 but the north pole of one utfracfs the south pole of another. 

 The attraction between the magnet and iron is mutual, for 

 the iron attracts the magnet as much as the magnet attracts 

 the iron ; since if they be placed on pieces of wood, so as to 

 float upon the surface of the water, it will be found that the 

 iron advances towards the magnet as well as the magnet to- 

 wards the iron, or, if the iron be kept steady, then the mag- 

 net will move towards it. 



