THE GERM OF THE ELECTRIC MOTOR.

49

"Sometimes, too," he says, "it happens that the nature of iron is repelled from this stone, being in the habit of flying from and following it in turns."

The allusion is now, not to the current which flows through the rings, but to the influence of the stone upon the iron, merely placed in its neighborhood-or, as we now say, in its "field of force" and not in contact with it. He is describing the turning of the ring, so as first to present one pole to the lodestone and then the other, for a ring usually has its poles located diametrically opposite each other. If the ring were supported so that its poles could be thus alternately presented to one and the same pole of the lodestone, then, whenever the ring pole was of the same name as that of the lodestone [as north pole to north pole, or south pole to south pole], the ring would be repelled, and would swing away from the lodestone; but if the ring pole were of different name from that of the lodestone [as north pole to south pole, or south pole to north pole], then the ring would be drawn to the lodestone, and if the latter were moved, the ring would follow it. Hence, by turning the ring to and fro, as on an axis, it could thus be made to swing or vibrate backwards or forwards in front of the lodestone, or, as Lucretius explains, the ring will fly from or follow the stone "in turns." Here is the first foreshadowing of the motion of an armature-for such is the ring-before the pole of a magnet, by change in relative polarity of magnet and armature; in the light of present knowledge we might even regard this as the advent into the world of the conversion of the energy of electricity into mechanical motion, and the germ of the electric motor.

Lucretius says, further, that he has seen the Samothracian rings "jump up" when the magnet stone had been "placed under." It is unquestionably true that in a suspended chain of rings, as he describes, the pole at the bottom of the lowest ring would be of the same name as that of the pole of the supporting lodestone—say, north. If

now, the same or north pole of a second lodestone were brought up to the lower part of that last ring, then that ring would be repelled and "jump up"-exactly as Lucretius says.

Even more remarkable than this is his statement that iron filings "will rave within brass basins" when the stone is placed beneath. This was the first perception of the field of force about a magnet by noting not merely the effect of its attraction or repulsion exerted upon the pole of another magnet brought into it, but upon loose iron filings free to dispose themselves therein along the lines of force. Then, under the astonished gaze of the poet, the particles of metal arranged themselves in the curious curves of the magnetic spectrum, and rose like bristles in front of the poles. And as he moved the stone beneathı the brass basin which held them, he saw them fly from one side of it to the other, sometimes grouping themselves for an instant in dense bunches, then leaping apart and scattering all so incoherently and so wildly, that it is small wonder that he regarded them as raving in their frantic desire to break away from the mysterious force. We shall find the performances of these raving iron filings astonishing the philosophers of the sixteenth century and remaining always a puzzle until Faraday and Maxwell found the key to it within our own time.

The explanation which Lucretius gives of magnetic attraction is repeated by Plutarch' who wrote a hundred and fifty years later and who applies it also to the amber attraction. He says, "that amber attracts none of those things that are brought to it, any more than the lodestone. That stone emits a matter which reflects the circumambient air and thereby forms a void. That expelled air puts in motion the air before it, which making a circle returns to the void space, driving before it towards the lodestone, the iron which it meets in its way." He then proposes a

1 Plutarch: Platonic Quaest., tom. 2.

difficulty "why the vortex which circulates around the lodestone does not make its way to wood or stone as well as iron," and, again like Descartes, answers, that "the pores of the iron have an analogy to the particles of the vortex circulating about the lodestone which yields them such access as they can find in no other bodies whose pores are differently formed."

Plutarch also refers to magnetic repulsion and says that "like as iron drawn by a stone often follows it, but often also is turned and driven away in the opposite direction, so also is the wholesome good and regular motion of the world."

It must not be assumed, because of the interpretations which it is possible to make at the present time of the magnetic phenomena mentioned by Lucretius, that any actual knowledge of the polarity of the lodestone existed in his day. Not until centuries later did this come to the civilized world.

Even when in course of time the recurrence of the repelling effect of the magnet attracted attention, no conception of polarity resulted. On the contrary, it was for a long time believed that the stone which repelled was a totally different stone from that which attracted iron. This supposed repelling stone is described for the first time by Pliny,' who calls it the "theamedes" and says that it comes from "Ethiopia, not far from Zmiris." For the first thirteen centuries of our era, belief in its existence was implicit. It served conveniently to explain magnetic repulsion, and hence, as frequently happens in such circumstances, it prevented investigation of that effect.

For discoveries concerning the amber, search may now be made through many centuries in vain. Plato, as has been stated, had linked together the attraction of the amber and the Heraclean stone, and Epicurus had attributed both to the same cause, namely, atoms and invisible

1 Pliny: lib. xxxvi. 25.

bodies outwardly projected from the attracting body combining with and bringing back the body attracted. That seems to have convinced the Greeks and Romans then, and the rest of the world for the ensuing two thousand years, that the amber and the magnet were interrelated; or, at all events, that they both attracted for exactly the same reason, and therefore nothing was to be gained by looking into the subject further. As for the Egyptians, it is doubtful whether they ever brought amber into extensive use at all, before quite a late period of their history. Only a few amber beads have been found in their tombs, and these last were of the 2d and 3d centuries of our era.1 The great Greek physician, Asclepiades,' recommends pills of amber as a specific for hemorrhages, and that seems to be the first medical use of the resin. His equally eminent brother of Rome has scant mention of it in his great work on materia medica.

3

All that the civilized world had learned concerning the lodestone and the amber has now been in substance stated. It is briefly summed up in the knowledge of the attractive capacity in each, of the ability of the magnet apparently to transfer its powers to iron, and of the existence of (supposedly) a kind of lodestone by which iron is repelled.

1 "An amber necklace, about 22 inches long, was also found in a grave here-one-third of it-the small beads only were kept at Bulak, as amber was almost, or quite, unknown in Egypt before." Tanis. 2d Memoir. Egypt. Explorat. Fund. W. F. Petrie. London, 1889. Per contra Clemens (Clem. Alex. Paedagog. iii. c. 2,) speaks of the sanctuary in Egyptian temples as shining "with gold, silver and amber." Possibly the word "amber" here is a mistranslation of the similar term for the electrum alloy. See Wilkinson: Anc. Egypt, i. 246, Boston, 1883.

3

2 Lib., vii., de Comp. Med. Time, circa 200 A. D.

Lib. de Simp. Med. See for this and preceding reference, Aldrevandus, Musaeum Metallicum, Bologna, 1648, p. 415.

CHAPTER III.

How or when the tendency of a freely-suspended magnet to set itself in a nearly north and south direction was first discovered is a question, the answer to which is probably forever lost. The civilized world remained in ignorance of the fact for nearly eighteen centuries after the attractive effect of the lodestone had become well known. Although, as I have already stated, it is not impossible to conjecture that the phenomenon was familiar to the ancestors of primitive civilization, who, from the highlands of Central Asia, dispersed in many races over the earth; yet the knowledge came to the people of the Middle Ages anew, through the invention of the first and greatest of electrical instruments-the mariner's compass; first, in its utilization of the mysterious force existing in the magnet; greatest, in that it has contributed more than any other product of human intelligence to the progress and welfare of mankind.

The obscurity which veils the discovery of the underlying principle of the compass in the remote past seems to extend to all the circumstances in which that contrivance originated. It has been ascribed to the Greeks, the Phœnicians, the Etruscans, the Egyptians and the Chinese. It is said to have first appeared on the ships of mediæval Italy, and yet to have been first known in mediæval France. It is also claimed as German, Arabian, English and Norse.

It is necessary to examine briefly the principal arguments advanced in behalf of these several nations. In this way we shall best perceive the conditions which caused progress or checked it, and so trace through its many channels the rise which we are following.