1^ MAGNETISM. 



using plates of a largo size ? — by multiplying the pairs of plaice ? G, 

 What is the invention of Prof Hare ? 7. What experiments may be 

 performed with it ? 8. What new view of the subject has Prof. Hare 

 offered ? (See the galvanic or voltaic battery described at the begin- 

 ning of this lesson, fig. 46.) [Note. Prof Hare has named his new 

 apparatus Calorimotor, or heat mover.] 



LESSON 72. 



Magnetism. 



Polar'ity, that property of a mngnet, by which, if left at liberty, 

 it will point towards the poles of the earth, or nearly so : the 

 same end always points to the same pole. 



Although the phenomena of the magnet have, for many 

 ages, engaged the attention of natural philosophers, not only 

 by their singularity and importance, but also by the obscu- 

 rity in which they are involved ; yet very few additions have 

 been made to the discoveries of the first inquiries into the 

 subject. No hypothesis has hitherto been framed, that will 

 account in an easy and satisfactory manner, for all the va- 

 rious properties of the magnet, nor have the links of the 

 chain, which connect it with the other phenomena of the 

 universe, ever been pointed out. It is certain, indeed, that 

 both natural and artificial electricity will give polarity to 

 needles, and even reverse a given polarity ; and hence it 

 may be inferred that there is a considerable affinity between 

 the electric and magnetic powers, but in what manner elec- 

 tricity acts in producing magnetism, is still utterly unknown. 



The ancients were acquainted with the attractive and re- 

 pulsive powers of the magnet ; but it does not appear that 

 they knew of its tendency to tiie pole : this very fortunate 

 discovery was made about the beginning of the fourteenth 

 century, when the spirit of exploring distant regions was 

 gradually forming in Europe. The use which might be 

 made of it in directing navigation was immediately perceived, 

 and that most valuable, but now familiar instrument, the 

 mariner's compass, invented. When navigators found that 

 they could, at all seasons, and in every place, discover the 

 north and south with the greatest ease and accuracy, it be- 

 came^no longer necessary to depend, like the voyagers of 

 former ages, merely on the light of the stars, and the obser 



