il'Z MAGNETISM. 



pin which is fixed in the centre of the box, and 

 upon which the needle, being properly balanced, 

 turns very easily. For common compasses, the 

 needles have a conical perforation made in the steel 

 itself, or in a piece of brass which is fastened in 

 the middle of the needle. 



The needle, which is balanced before it is mag- 

 netized, will lose its balance by that process, on 

 account of the dipping; therefore, a small weight, 

 or moveable piece of brass, is placed on one side 

 of the needle, by the shifting of which, either 

 nearer to, or farther from, the centre, the needle 

 will always be balanced. 



The azimuth compass is one to which two sights 

 are adapted, through which the sun is to be seen, 

 in order to find its azimuth, and from thence to 

 ascertain the declination of the magnetic needle at 

 the place of observation. 



The cause of magnetism is entirely unknown to 

 us, nor has any thing farther than mere hypotheses 

 been advanced to account for this, as well as every 

 other species of attraction. 



Aepinus supposed that there exists a peculiar 

 fluid, which he called the magnetic fluid, so subtile 

 as to penetrate all bodies ; that its particles are 

 repulsive of each other ; also, that there is a 

 mutual attraction between this fluid and iron, 

 but that no other substance has any action 

 upon it. 



