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SCIENCE PROGRESS 



represents its magnetic power, assuming that of steel to be 

 100,000 : 



The above list is a very incomplete representation of Delesse's 

 results. In many cases he compared the different varieties of 

 a mineral, and the results exhibited considerable variation due 

 to differences in composition and the amount of impurity. For 

 this reason, the numbers given in the above list cannot be 

 regarded as being exact in their significance, especially when 

 they are considered apart from the composition and physical 

 condition of the minerals concerned ; but they serve to illustrate, 

 in a general way, the variable magnetic permeability among 

 minerals. 



Delesse exercised caution in making his comparative 

 measurements, and avoided errors due to variation in current, 

 etc. The inconstancy of the current generated by his battery 

 led him to suggest that it was preferable to use a strong 

 permanent magnet in making observations on the comparative 

 magnetic powers of minerals. He pointed out that a compound 

 horseshoe magnet was quite powerful enough for the purpose, 

 while it had also the great advantage of being constant. 



His comments on the peculiarities exhibited by the different 

 groups of minerals are very interesting. These comments were 

 based largely on the view that the chemical constituents of 

 a mineral asserted their separate magnetic effects, even in a 

 state of combination. Thus he observed that the presence of 

 iron, manganese, cerium, and other paramagnetic elements tends 

 to increase the magnetic power of a mineral, while the presence 

 of silica, alumina, lime, water, fluorine, and other diamagnetic 

 constituents tends to diminish it. A broad survey of minerals 



