cfi Thoughts on Magnetifm, 



be inferted into It, the Glauber alone will cryftalize, Do not thefe experiments fully evince 

 both the attradive and repulfive powers, not only of different falls but of different furfaces 

 of the fame fait ? 



11. Thefe powers within their proper fpliere of action have been found indefinitely 

 great ; thus water confined in cannon feveral inches thick, and expofed to a degree of cold 

 much beneath the freezing point, has been obferved to cryftalize into ice that burft the me- 

 tallic impediment oppofed to the form it then afTumes. 



12. The vaft difference however attending the developement of thefe two powers (of mag- 

 netifm and cryftalization) will undoubtedly flrike many as an infuperable objection to their 

 identity, yet their direBion in all its varieties being exadlly the fame, difference in other 

 circumftances feems to me to indicate rather a variety of degrees, in the fame power, than 

 any effential difference in the powers themfelves. 



I novf come to the application of the above principles to the magnetic phsenomena. Thefe 

 may in general be reduced to the following, viz. AttraEiion, Repulfton, Polarity. 

 Communication. 

 Declination. 

 Inclination. 



Exclujive appropriation to Iron. 

 DeJlruSlion of the Magnetic power. 



jjl, AttraBion, Repuljton, Polarity. 



The quantity of iron found on and within fuch parts of the furface of the globe as wc 

 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 proportion of from 2 to 1 8 or 20 per cent, 

 and perhaps at a medium we may flate it in all of them at 6 per cent. ; moreover its own 

 ores are of all others the mod common and the molt copious ; in many places, particularly 

 in the moft northern climates, whole mountains of it are found, and many of them mag- 

 netic. 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, notwithftanding the immenfe quantity 

 of water that covers the greater part of its furface to conGderable unknown depths, and not- 

 withftanding that the fpecific gravity of by far the greater part of the ftones and earths it 

 contains docs not exceed and fcarcely amounts even to three times the weight of an equal 

 bulk 6f water, and that the quantity of mineral fubftances whofe fpecific weight exceeds 

 four times that of water is almoft infinitely fmall in comparifon to the other known com- 

 ponent parts of the globe," and finally that the weight of moft iron ores is about four or five 

 times that of water; all this I fay confidered, it is difficult to avoid concluding that the 

 interior part of the globe confifts chiefly of iron ore difpofed in one or more aggregate 

 inaffes ; a conclufion that is farther confirmed, on reflefting that volcanic lavas eje£l:ed 

 4 from 



