HISTORY OF DISCOVERY RELATIVE TO MAGNETISM. 293 



of the most interest to us at present, is dated March 4, 1544, and contains accu- 

 rate descriptions of three magnetic discoveries which Hartmann had shown the 

 year before, at Nuremberg, to Ferdinand, King of Bohemia, a brother of Charles 

 V. This letter is found in the secret archives at Berlin, and was published 

 by Mosor. Hartmann states in this that he had discovered that the extremity 

 of the needle, which is intended to point to the north, must be rubbed with the 

 end of the stone which points to the south, and that a needle so rubbed which 

 has previously been accurately balanced so as to rest horizontally, will, after 

 the magnetization, incline or dip at one end below the horizon. Further, that 

 a large bar of iron placed vertically becomes so strongly magnetic as to repel 

 with its lower end the northern point of a compass needle. This fact is best 

 shown by using a large bar and a small needle. 



The fact that rusted ii-on bars, which have remained for a long time in a 

 vertical position, exhibit always more or less magnetism, was first observed in 

 1590 by Julius Cwsar, a surgeon, at Rimini, who observed that an iron rod, 

 which had been placed for the support of the wall of the tower of the church of 

 the Augustines, had become magnetic. Gassendi observed the same, in 1G30, 

 in an iron cross which had been 'thrown down by lightning from the church 

 tower at Aix. He found that the rusted extremities of this cross had the qual- 

 ities of the loadstone. When, about the year 1722, the iron cross whigh had 

 adorned for several centuries the spire of the church tower at Delft was taken 

 down for repair, the celebrated Loewenhoeck, on the suggestion of a stranger, 

 as he says, obtained a piece of the iron from one of the laborers, but no influ- 

 ence was exhibited by it on the compass needle. Some time afterwards, Ifowever, 

 the same laborer brought him a rusted piece from the foot of the vertical bar, 

 which exhibited more powei" of attraction than the two natural magnets which 

 Loewenhoeck possessed. 



Whilst magnetism made but slow progress by incidental observations, it re- 

 ceived suddenly a powerful impulse from the investigations of Dr. William 

 Gilbert, of Colchester, England. This distinguished individual, who was phy- 

 sician to Queen Elizabeth, published in 1600 his "Dissertation on the Physiology 

 of the Magnet," a work which not only contained everything known of magnet- 

 ism and electricity up to that period, arranged in a truly scientific manner, but 

 also a numerous and ingenious series of investigations on the subject by himself. 

 He was the first who advanced the proposition that the earth itself acts, in all 

 its parts, as a great magnet, in opposition to the opinions of those who, either 

 with Olaus Magnus, supposed that there existed great magnetic mountains of 

 such power that ships, in the construction of which iron had not been entirely 

 omitted, Avould be attracted and held fast, or with those who placed the power 

 of attraction in the sky, as, for instance, the astrologer, Lucas Gauricus, who 

 supposed that a great magnet existed under the tail of Ursa Major, a constella- 

 tion in the northern hemisphere to which all compass needles pointed. Gilbert 

 logically refuted these and similar fanciful hypotheses? and substituted his own 

 rational theory in their stead — a theory which, in its general principles, has 

 been retained to the present time. He also attempted to explain, but with less 

 success, the declination of the needle by ascribing magnetism merely to the 

 solid parts of the earth, and not to the water, so that the needle would incline 

 towards the continent, because a greater amount of magnetic power existed there. 



It could, moreover, not escape the sagacity of a man like Gilbert, that the 

 magnetic terminology, as he found it, was liable to great inconsistencies. Even 

 in our days we are still accumstomed to call the end of the needle which points 

 to the north its north pole, and the one pointing to the south its south pole. 

 This form of expression is, nevertheless, incorrect, for if we admit that the 

 earth is a great magnet, and that in the vicinity of the geographical north pole 

 a magnetic north pole is situated, this north pole could only attract the south 

 pole of another magnet, and consecyiently the end of the magnetic needle 



