CES ARE'S DISCOVERY. 227 



the mass of the latter: also the inversion of polarity which 

 may take place during the magnetization of the needle, 

 although he seems to have known nothing of consequent 

 poles: also magnetic variation (but not the variation of the 

 variation) and magnetic inclination: also the magnetic 

 properties acquired by iron u freely exposed to the air." 



Robert Norman's book, to which I have referred in the 

 preceding chapter, was published a few years before Sarpi 

 is believed to have made his principal magnetical investi- 

 gations; and it is altogether unlikely that it escaped the 

 friar's attention. The Letter of Peregrinus had been in 

 print for more than two decades. Moreover, a manuscript 

 of it existed, and was at Sarpi' s disposal in the Castellan 

 Library of Venice. We are therefore justified in eliminat- 

 ing from the two categories, before given, all matters 

 anticipated by Norman and Peregrinus, so far as these can 

 be recognized. This done, the net result is to leave the 

 destruction of magnetism by fire, the magnetization of 

 iron by means other than induction from a lodestone 

 afterwards alluded to as the acquirement of magnetic prop- 

 erties by iron freely exposed to air and the existence of 

 the field of force around the magnetic poles, now directly 

 made known for the first time. 



That a lodestone could be deprived of its attractive 

 quality by heating it to a high temperature was a new 

 discovery, which may well have excited the incredulity of 

 those who believed with Norman that the virtue in the 

 stone was implanted by Providence, and hence was pre- 

 sumably ineradicable. The revelation that iron could be 

 magnetized without the aid of the stone at all was not 

 original with Sarpi, but was the result of an accidental 

 observation made by one Giulio Cesare, a surgeon of 

 Rimini, early in 1586, and not long before Sarpi wrote 

 concerning it. An iron rod which supported a terra-cotta 

 ornament upon the tower of a church in the before-named 

 town had become bent by the force of the wind, and had 

 remained thus distorted for about ten years. It was taken 



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