238 THE INTELLECTUAL RISE IN ELECTRICITY. 



now briefly be stated. The destruction of magnetization 

 by high temperature seems to have been found by burning 

 the lodestone, which, when surrounded by heaped-up coals, 

 em its a u blue, sulphurous and iron flame; and, at the same 

 time, with the dissipation of this, the soul of the magnet 

 departs and it loses its attractive power." The suggestion 

 by Peregrinus of -measuring the force of the magnet is car- 

 ried into practical effect, and the strength determined is 

 that required to resist separation of the armature from the 

 magnet, which is arranged in one pan of a balance. The 

 fact is noted that, while the magnetic virtue passes freely 

 through brass, etc., iron acts as a screen to cut it off. The 

 guarding of compass needles after they are magnetized 

 from proximity with lodestones is strongly advised, lest 

 "they be inebriated;" and clean iron is said to receive the 

 virtue much more tenaciously than metal containing rust 

 or earthy matters. Here occurs the first mention of the 

 fact that u sailors prefer steel" for compass needles 

 " which will keep its value for a hundred years." Iron 

 filings, we are told, wrapped in paper, receive virtue like a 

 solid magnet, but, if they are shaken, they lose it. 



Porta's recital abounds in absurdities, many of which 

 are due to experimental errors. His theory of the cause 

 of the attraction of the lodestone is correlated to the ob- 

 served behavior of the iron filings; for he considers the 

 magnetic forces to be due to minute particles of the stone 

 springing from friction and concentrated into hairs, which, 

 becoming attached to iron, impart thereto magnetic virtue. 

 Yet, on the other hand, he believed with Alexander of 

 Aphrodiseus that the lodestone actually fed on iron, and 

 therefore buried a stone surrounded by filings and occasion- 

 ally exhumed it to note without success the amount de- 

 voured. He imagined that iron rubbed by a diamond 

 would become magnetic, and so avers; and, he believed 

 that a magnet has east and west, as well as north and south, 

 poles. A closer analysis of his work will show many more 

 such delusions, and, to counterbalance them, suggestions 

 which perhaps proved the germs of later useful discoveries. 



