[ i8, ] 



I NOW come to the application of the above principles to the- 

 magnetic phasnomena. Thefe may in general be reduced to the 

 following, viz. AttraBlonyReptdfion^ Polarity. 



Communication . 



Declination. 



Inclination. 



Excltijive appropriation to Iron. 



Deft r union of the Magnetic power. 



i/?, AttraElion., Repulfion., Polarity. 



The quantity of iron found on and within fuch parts of the 

 furface of the globe as we are acquainted with, far furpaffes that 

 of any other mineral fubftance fingly taken, or even of many of 

 them taken together ; fcarce any ftone or metallic ore or earth is 

 found free from it ; it enters into their compofition in the propor- 

 tion of from 2 to 1 8 or 20 per cent, and perhaps at a medium we 

 may ftate it in all of them at 6 per cent.; moreover its otvn ores 

 are of all others the moft common and the mofi: copious ; in many 

 places, particularly in the moft northern climates, whole moun- 

 tains of it are found, and many of them magnetic. When to 

 this confideration we add that of the fpecific gravity of the globe, 

 which has been found to be 4,5 times heavier than water, not- 

 withftanding the immcnfe quantity of water that covers the 

 greater part of its furface to confiderable unknown depths, and 



notwithftanding 



