The use of iron filings to map out the entire field of force that surrounds a magnet was unknown to classical antiquity; it was not known to Peregrinus or Roger Bacon in the thirteenth century or even to Gilbert in the sixteenth. The credit for reviving the use of filings and employing them to show the direction of the resultant force at any point in the neighborhood of a magnet, belongs to Cabeo, an Italian Jesuit, who described and illustrated it in his "Philosophia Magnetica," published at Ferrara in the year 1629. On page 316 of that celebrated work will be found a figure, the first of the kind, showing the position taken by the filings when plentifully sifted over a lodestone: thick tufts at the polar ends with curved lines in the other parts of the field.
The Samothracian rings mentioned in the passage quoted above were light, hollow rings of iron which, for the amusement of the crowd, the jugglers of the times held suspended one from the other by the power of a lodestone.
Writing of the lodestone, Lucretius says:
Its viewless, potent virtues men surprise,
Its strange effects, they view with wond'ring eyes,
When without aid of hinges, links or springs
A pendent chain we hold of steely rings.
Dropt from the stone—the stone the binding source—
Ring cleaves to ring and owns magnetic force;
Those held above, the ones below maintain;
Circle 'neath circle downward draws in vain
Whilst free in air disports the oscillating chain.
Though the Roman poet was acquainted with two of the leading properties of the lodestone, viz., attraction and repulsion, there is nothing in the lines quoted above or in any other lines of his great didactic poem to indicate that he was aware of the remarkable difference which there is between one end of a lodestone and the other. The polarity of the magnet, as we term it, was unknown to him and remained unknown for a period of 1200 years.
During that long period nothing of importance was added to the magnetic lore of the world. True, a few fables were dug out of the tomes of ancient writers which gained credence and popularity, partly by reason of the fondness of the human mind for the marvelous, and partly also by reason of the reputation of the authors who stood sponsors for them.
Pliny (23-79 A. D.) devotes several pages of his "Natural History" to the nature and geographical distribution of various kinds of lodestones, one of which was said to repel iron just as the normal lodestone attracts it. Needless to say that the mineral kingdom does not hold such a stone, although Pliny calls it theamedes and says that it was found in Ethiopia.
Pliny is responsible for another myth which found favor with subsequent writers for a long time, when he says that a certain architect intended to place a mass of magnetite in the vault of an Alexandrian temple for the purpose of holding an iron statue of Queen Arsinoe suspended in mid-air. Of like fabulous character is the oft-repeated story about Mahomet, that an iron sarcophagus containing his remains was suspended by means of the lodestone between the roof of the temple at Mecca and the ground.
As a matter of fact, Mahomet died at Medina and was buried there in the ordinary manner, so that the story as currently told of the suspension of his coffin in the "Holy City" of Mecca, contains a twofold error, one of place and the other of position. By a recent (1908) imperial irade of the Sultan of Turkey, the tomb is lit up by electric light in a manner that is considered worthy of the "Prophet of Islam."
Four centuries after Pliny, Claudian, the last of the Latin poets as he is styled, wrote an idyl of fifty-seven lines on the magnet, which contains nothing but poetic generalities. St. Ambrose (340-397) and Palladius (368-430), writing on the Brahmans of India, tell how certain magnetic mountains were said to draw iron nails from passing ships and how wooden pegs were substituted for nails in vessels going to Taprobane, the modern Ceylon. St. Augustine (354-430) records in his "De Civitate Dei" the wonder which he felt in seeing scraps of iron contained in a silver dish follow every movement of a lodestone held underneath.