Beacon Lights of History Volume Xiv Part 14

And one region yet remains to be considered, the scattered coasts and islands that owned the Greek speech, and that created the Greek civilization. It is not the Greece of the Parthenon and Pericles that we wish to discover, for that we fairly know; but the arts and the history of those earlier Greeks and Trojans that Homer tells of, the age of Agamemnon and Ulysses, of Helen and Hector and Priam, and of the yet earlier tribes that sailed the Aegean, and settled the Mediterranean islands, and sent their s.h.i.+ps to the Egyptian coasts, and sought golden fleeces on the Euxine Sea. All about the coast of Asia Minor they lived, while that Hitt.i.te power was ruling the interior; and, intermixed with Phoenician trading-posts, they held the great islands of Crete and Cyprus and the sh.o.r.es of Sicily and Italy. What shall we call them? Were they Dorians, or Heraclidae, Achaeans or Pelasgi? Were they of the same race as the mysterious Etruscans, or shall we name them simply Mycenaeans, as we call the art Mycenaean that ruled the islands and coasts down to the Homeric age, and we know not how many centuries earlier, but certainly as far back as the conquering period of the Eighteenth Egyptian Dynasty of Thothmes? Their soldiers and merchants and their fine vases are pictured on the walls of Egypt, and their pottery has long been studied; but we knew little of them until Dr.

Schliemann, the Greek merchant who achieved wealth in the United States, bravely opened the great ruins of Troy, in the full patriotism of his a.s.surance that Homer's story of the Trojan war was history as well as poetry. As he found one burnt and buried city under another,--for many times was Troy destroyed,--and extended his investigations to Tiryns and other ancient cities, one volume of splendid research followed another, until the trader had compelled the unwilling scholar to confess that he must dig for both history and art. To be sure, his interpretations were quite too literal at first, but the whole world of cla.s.sical scholars.h.i.+p has learned from him the new method of research. Splendid have been the results. If we are not sure which stratum represents the city of Priam, we do learn how the people lived, and how fine was their work in silver and gold, and how slight their knowledge of letters. Dr. Schliemann has now a mult.i.tude of imitators. France and Germany and England and the United States each maintain a school of archaeology in Athens, and each conducts careful explorations. Our American School lost to the French, for lack of money at the right time, the chance to explore Delphi, but it has carried on careful explorations at Corinth and other places. How wonderful was the discovery, not long ago, of a s.h.i.+pload of bronze and marble statues wrecked while being transported as spoil of war from Corinth to Rome!

But the most surprising discoveries in the realm of old Greek history and art are those that have been made in these last two or three years in Crete. Crete was a famous centre of ancient Greek legend. Jupiter was born and reared on Mount Ida. From another mountain summit in Crete the G.o.ds watched the battle on the plains of Troy. There ruled Minos, who first gave laws to men, and who at his death was sent by the G.o.ds to judge the shades as they entered the lower world. There was the famous Labyrinth, and there the Minotaur devoured his annual tale of maidens until he was slain by Theseus. Was there such a real palace of Minos as the Greek poets sung? The magnificent palace of the Cretan kings at Cnossus has been found, by Mr. Evans, with its friezes, its spiral ornaments, its flounce-petticoated women, its treasuries, and its tablets written in a script so old that it cannot yet be read, but which will be read as surely as scholars.h.i.+p leaves none of its riddles unsolved. The childhood of Greece, its mighty infancy, out of which it grew to be the creator and the example of all the world's culture, is even now being exposed to our view, safely kept to be recovered by the scholars of our generation.

Of interest rather to the student of the curiosities of history are the mounds and pyramids and temples built by the aborigines of America; for these tribes have had absolutely no part in creating our dominant civilization or developing its art. China and j.a.pan are, at this late day, giving something to the world's store of beauty and utility; but the mound-builders and cliff-dwellers, the Mayas and Toltecs and Incas, have given absolutely nothing which the world cared to accept. But this does not argue that it is not worth while to learn what we can of the rude civilization of the races whom we have displaced. Their arrowheads and hatchets are in every little museum. Their mounds, sometimes shaped like serpents or tortoises or lizards, are scattered over all the central States, and many of them have been carefully explored with scanty results. The cliff-dwellers have left somewhat richer remains, more baskets and parched corn, yet nothing of artistic value. We have to go to Mexico and Yucatan and further south to Peru, to find the majestic capitals of the Mayas and Incas, who had really reached a fair degree of such civilization as stone and copper, without iron, and the beginnings of picture symbols, without letters, could provide. Humboldt and Stephens, and Lord Kingsborough, and Squier, and Tchudi, and Charnay have made explorations and found vast and wonderful cities, some of them deserted and overgrown before Cortez and Pizarro took possession of the lands for Spain and enslaved the people. Where the city of Mexico now stands was a famous capital, from whose ruins were taken the great Calendar stone and the double statue of the G.o.d of war and the G.o.d of death. In Palenque and Uxmal, capitals of Yucatan, were immense palaces and temples, with the weird ornamentation of Mayan imagination; and equal wonders exist in the high uplands where the Incas ruled Peru. Even their barbaric art and their unrecorded history must be recovered, to satisfy the curiosity of the more fortunate races whose boasted Christianity visited on them nothing better than cruel slaughter. At least we can give them museums and publish magnificent pictures of their ruins.

So we may bless the ashes and sand that seemed to destroy and bury the monuments of the mighty empires of the ancient world, but which have kindly covered and preserved them, just as we put our treasures away in some safety-vault while absent on a long journey. The fire burned the upper wooden walls of the city, and it fell in ruins, but under those ruins, covered by that ashes, were preserved for two thousand, three thousand, five thousand years uninjured, the choicest sculpture and the most precious records of ancient nations,--retained beyond the reach of vandal hands, until scholars.h.i.+p had grown wise enough to ask questions of forgotten history, and had sent Layard and Schliemann and De Sarzec and Evans and a hundred other men to dig with their compet.i.tive spades.

But in all the long list of enthusiasts not one deserves a higher honor or has reaped a richer harvest than Sir Henry Layard.

AUTHORITIES.

Layard: "Early Adventures;" "Nineveh and its Remains;" "Nineveh and Babylon;" "Monuments of Nineveh." Botta: "Monument de Ninive." Loftus: "Chaldea and Susiana." Y. Place: "Ninive et a.s.syrie." Hilprecht: "Babylonian Expedition of the University of Pennsylvania;" "Recent Research in Bible Lands." Perrot and Chipiez: "History of Art in Antiquity." J.P. Peters: "Nippur." R.W. Rogers: "History of Babylonia and a.s.syria." F. Lenormant: "Students' Manual of the Ancient History of the East;" "The Beginnings of History." Maspero: "Dawn of Civilization;"

"Struggle of the Nations;" "Pa.s.sing of the Empires;" "Egyptian Archaeology;" "Life in Ancient Egypt and a.s.syria." C.J. Ball: "Light from the East." Egypt Exploration Fund's Publications. F.J. Bliss: "Exploration in Jerusalem;" "A Mound of Many Cities." Schliemann: "Troy and its Remains;" "Ilios;" "Mycenae;" "Tiryns;" "Troja." A.J. Evans: "Cnossus;" "Cretan Pictographs." Tsountas and Manatt: "The Mycenaean Age."

MICHAEL FARADAY.

1791-1867.

ELECTRICITY AND MAGNETISM.

BY EDWIN J. HOUSTON, PH.D.

"No man is born into the world whose work Is not born with him. There is always work, And tools to work withal, for those who will."

LOWELL

A man was born into the world, on the 22d of September, 1791, whose work was born with him, and who did this work so well that he became one of its greatest benefactors. Indeed, much of the marvellous advance made in the electric arts and sciences, during the last half-century, can be directly traced to this work.

It was in Newington b.u.t.ts, in London, England, that the man-child first opened his eyes on the wonders of the physical world around him. To those eyes, in after years, were given a far deeper insight into the mysteries of nature than often falls to the lot of man. This man-child was Michael Faraday, who has been justly styled, by those best capable of judging him, "The Prince of Experimental Philosophers."

The precocity so common in the childhood of men of genius was apparently absent in the case of young Faraday. The growing boy played marbles, and worried through a scant education in reading, writing, and arithmetic, unnoticed, and most probably, for the greater part, severely left alone, as commonly falls to the lot of nearly all boys, whether ordinary or extraordinary. At the early age of thirteen, he was taken from school and placed on trial as errand-boy in the book-shop of George Ribeau, in London. After a year at this work, he was taken as an apprentice to the book-binding trade, by the same employer, who, on account of his faithful services, remitted the customary premium. At this work he spent some eight years of his life.

But far be it from us even to hint at the absence of genius in the young child. Genius is not an acquired gift. It is born in the individual.

Apart from the marvellous achievements of the man, a mere glance at the magnificent head, with its high intellectual forehead, the firm lips, the intelligent inquiring eyes, and the bright face, as seen in existing pictures, a.s.sures us that they portray an unusual individuality, incompatible with even a suspicion of belonging to an ordinary man.

Doubtless the growing child did give early promise of his future greatness. Doubtless he was a formidable member of that terrible cla.s.s of inquiring youngsters who demand the why and the wherefore of all around them, and refuse to accept the unsatisfactory belief of their fathers that things "are because they are." In its self-complacency, the busy world is too apt to fail to notice unusual abilities in children,--abilities that perhaps too often remain undeveloped from lack of opportunities. But whether young Faraday did or did not, at an early age, display any unusual promise of his life-work, all his biographers appear to agree that he could not be regarded as a precocious child.

Faraday disclaimed the idea that his childhood was distinguished by any precocity. "Do not suppose that I was a very deep thinker, or was marked as a precocious person," says Faraday, when alluding to his early life.

"I was a very lively, imaginative person, and could believe in the 'Arabian Nights' as easily as the 'Encyclopaedia,' but facts were important to me, and saved me. I could trust a fact and always cross-examined an a.s.sertion. So when I questioned Mrs. Marcet's book [he is alluding to her 'Conversations on Chemistry'], by such little experiments as I could find means to perform, and found it true to the facts as I could understand them, I felt that I had got hold of an anchor in chemical knowledge, and clung fast to it."

But while there may be a question as to the existence of precocity in the young lad, there does not appear to be any reason for believing that his unusual abilities were the result of direct heredity. His father, an ordinary journeyman blacksmith, never exhibited any special intellectual ability, though possibly poverty and poor health may have been responsible for this failure. His mother, too, it appears, was of but ordinary mentality.

The environment of those early years--that is, from 1804 to 1813, while in the book-binding business--was far from calculated to develop any marked abilities inherent in our young philosopher. What would seem less calculated to inspire a wish to obtain a deeper insight into the mysteries of the physical world than the trade of book-binding, especially in the case of a boy whose scholastic education ceased at fourteen years and was limited to the mere rudiments of learning? But, fortunately for the world, the inquiring spirit of the lad led him to examine the inside of the books he bound, and thus, by familiarizing himself with their contents, he received the inspiration that good writing is always ready to bestow on those who properly read it. Two books, he afterwards informs us, proved of especial benefit; namely, "Marcet's Conversations on Chemistry," already referred to, and the "Encyclopaedia Britannica." To the former he attributes his grounding in chemistry, and to the latter his first ideas in electricity, in both of which studies he excelled in after years. As we have seen, even at this early age he followed the true plan for the physical investigator, cross-questioned all statements, only admitting those to the dignity of facts whose truth he had established by careful experimentation.

But our future experimental philosopher has not as yet fairly started on the beginnings of his life-work. The possibilities of the book-binding trade were too limited to permit much real progress. A circ.u.mstance occurred in the spring of 1812 that shaped his entire after-life. This was the opportunity then afforded him to attend four of the last lectures delivered at the Royal Inst.i.tution, by the great Sir Humphry Davy. Faraday took copious notes of these lectures, carefully wrote them out, and bound them in a small quarto volume. It was this volume, which he afterwards sent to Davy, that resulted in his receiving, on March 1, 1813, the appointment of laboratory a.s.sistant in the Royal Inst.i.tution.

His pay for this work was twenty-five s.h.i.+llings a week, with a lodging on the top floor of the Inst.i.tute, a very fair compensation for the times.

Very congenial were the duties of the young a.s.sistant. They were to keep clean the beloved apparatus of the lecturers, and to a.s.sist them in their demonstrations. The new world thus opened was full of bright promise. He keenly felt the deficiencies of his early education, and did his best to extend his learning, so that he might be able to make the most of his opportunities. But what he perhaps appreciated the most was the inspiration he received from the great teacher Davy, who was then Professor of Chemistry and Director of the Laboratory of the Royal Inst.i.tution; for Faraday a.s.sisted at Davy's lectures, and in an humble way even aided his investigations, sharing the dangers arising from the explosion of the unstable substance, chloride of nitrogen, that Davy was then investigating. Faraday has repeatedly acknowledged the debt owed to the inspiration of this teacher. Davy also, in later life generously recognized, in his former a.s.sistant, a philosopher greater than himself.

As the renowned astronomer, Tycho Brahe, discovered in one of his pupils, John Kepler, an astronomer greater than the master, and as Bergman, the Swedish chemist, in a similar manner, discovered the greater chemist Scheele, so when Davy, in after years, was asked what he regarded as his greatest discovery, he briefly replied, "Michael Faraday."

The task of the scientific historian, who endeavors honestly to record the progress of research, and to trace the influence of the work of some individual on the times in which he lived, is by no means an easy one; for, in scientific work one discovery frequently pa.s.ses so insensibly into another that it is often difficult to know just where one stops and the other begins, and much difficulty constantly arises as to whom the credit should be given, when, as is too often the case, these discoveries are made by different individuals. It is only when some great discovery stands alone, like a giant mountain peak against the clear sky, that it is comparatively easy to determine the extent and character of its influence on other discoveries, and justly to give the credit to whom the credit is due. Such discoveries form ready points of reference in the intellectual horizon, and mark distinct eras in the world's progress. This is true of all work in the domain of physical science, but it is especially true in that of electricity and magnetism, in which Faraday was pre-eminent. The scope of each of these sciences is so extended, the number of workers so great, and the applications to the practical arts so nearly innumerable, that it is often by no means an easy task correctly to trace their proper growth and development.

Faraday's investigations covered vast fields in the domain of chemistry, electricity, and magnetism. It is to the last two only that reference will here be made. Faraday's life-work in electricity and magnetism began practically in 1831, when he made his immortal discovery of the direct production of electricity from magnetism. His best work in electricity and magnetism was accomplished between 1831 and 1856, extending, therefore, over a period of some twenty-five years, although it is not denied that good work was done since 1856. Consequently, it was at so comparatively recent a date that most of Faraday's work was done that some of the world's distinguished electricians yet live who began their studies during the latter years of Faraday's life. The difficulties of tracing, at least to some extent, the influence that Faraday's masterly investigations have had on the present condition of the electrical arts and sciences will, therefore, be considerably lessened.

The extent of Faraday's researches and discoveries in magnetism and electricity was so great that it will be impossible, in the necessarily limited s.p.a.ce of a brief biographical sketch, to notice any but the more prominent. Nor will any attempt be made, except where the nature of the research or discovery appears to render it advisable, to follow any strict chronological order; for, our inquiry here is not so much directed to a mere matter of history as to the influence which the investigation or discovery exerted on the life and civilization of the age in which we live.

There is a single discovery of Faraday that stands out sharply amidst all his other discoveries, great as they were, and is so important in its far-reaching results that it alone would have stamped him as a philosophical investigator of the highest merits, had he never done anything else. This was his discovery of the means for developing electricity directly from magnetism. It was made on the 29th of August, 1831, and should be regarded as inspired by the great discovery made by Oersted in 1820, of the relations existing between the voltaic pile and electro-magnetism. It was in the same year that Ampere had conducted that memorable investigation as to the mutual attractions and repulsions between circuits through which electric currents are flowing, which resulted in a theory of electro-magnetism, and finally led to the production of the electro-magnet itself. Ampere had shown that a coil of wire, or helix, through which an electric current is pa.s.sing, acted practically as a magnet, and Arago had magnetized an iron bar by placing it within such a helix.

In common with the other scientific men of his time, Faraday believed that since the flow of an electric current invariably produced magnetism, so magnetism should, in its turn, be capable of producing electricity. Many investigators before Faraday's time had endeavored to solve this problem, but it was reserved to Faraday alone to be successful. Since success in this investigation resulted from some experiments he made while endeavoring to obtain inductive action on a quiescent circuit from a neighboring circuit through which an electric current was flowing, we will first briefly examine this experiment. All his experiments in this direction were at first unsuccessful. He pa.s.sed an electric current through a circuit, which was located close to another circuit containing a galvanometer,--a device for showing the presence of an electric current and measuring its strength,--but failed to obtain any result. He looked for such results only when the current had been fully established in the active circuit. Undismayed by failure, he reasoned that probably effects were present, but that they were too small to be observed owing to the feeble inducing current employed. He therefore increased the strength of the current in the active wire; but still with no results.

Again and again he interrogates nature, but unsuccessfully. At last he notices that there is a slight movement of the galvanometer needle at the moment of making and breaking the circuit. Carefully repeating his experiments in the light of this observation, he discovers the important fact that it is only at the moment a current is increasing or decreasing in strength--at the moment of making or breaking a circuit--that the active circuit is capable of producing a current in a neighboring inactive circuit by induction. This was an important discovery, and in the light of his after-knowledge was correctly regarded as a solution of the production of electricity from magnetism.

Observing that the galvanometer needle momentarily swings in one direction on making the circuit, and in the opposite direction on breaking it, he establishes the fact that the current induced on making flows in the opposite direction to the inducing current, and that induced on breaking flows in the same direction as the inducing current.

Having thus established the fact of current induction, he makes the step of subst.i.tuting magnets for active circuits; a simple step in the light of our present knowledge, but a giant stride at that time. Remembering that current induction, or, as he called it, voltaic current induction, takes place only while some effect produced by the current is either increasing or decreasing, he moves coils of insulated wire towards or from magnet poles, or magnet poles towards or from coils of wire, and shows that electric currents are generated in the coils while either the coils or the magnets are in motion, but cease to be produced as soon as the motion ceases. Moreover, these magnetically induced currents differ in no respects from other currents,--for example, those produced by the voltaic pile,--since, like the latter, they produce sparks, magnetize bars of steel, or deflect the needle of a galvanometer. In this manner Faraday solved the great problem. He had produced electricity directly from magnetism!

With, perhaps, the single exception of the discovery by Oersted, in 1820, of the invariable relation existing between an electric current and magnetism, this discovery of Faraday may be justly regarded as the greatest in this domain of physical science. These two master minds in scientific research wonderfully complemented each other. Oersted showed that an electric current is invariably attended by magnetic effects; Faraday showed that magnetic changes are invariably attended by electric currents. Before these discoveries, electricity and magnetism were necessarily regarded as separate branches of physical science, and were studied apart as separate phenomena. Now, however, they must be regarded as co-existing phenomena. The ignorance of the scientific world had unwittingly divorced what nature had joined together.

In view of the great importance of Faraday's discovery, we shall be justified in inquiring, though somewhat briefly, into some of the apparatus employed in this historic research. Note its extreme simplicity. In one of his first successful experiments he wraps a coil of insulated wire around the soft iron bar that forms the armature or keeper of a permanent magnet of the horse-shoe type, and connects the ends of this coil to a galvanometer. He discovers that whenever the armature is placed against the magnet poles, and is therefore being rendered magnetic by contact therewith, the deflection of the needle of the galvanometer shows that the coiled wire on the armature is traversed by a current of electricity; that whenever the armature is removed from the magnet poles, and is therefore losing its magnetism, the needle of the galvanometer is again deflected, but now in the opposite direction, showing that an electric current is again flowing through the coiled wire on the armature, but reversed in direction. He notices, too, that these effects take place only while changes are going on in the strength of the magnetism in the armature, or when magnetic flux is pa.s.sing through the coils; for, the galvanometer needle comes to rest, and remains at rest as long as the contact between the armature and the poles remains unbroken.

In another experiment he employs a simple hollow coil, or helix, of insulated wire whose ends are connected with a galvanometer. On suddenly thrusting one end of a straight cylindrical magnet into the axis of the helix, the deflection of the galvanometer needle showed the presence of an electric current in the helix. The magnet being left in the helix, the galvanometer needle came to rest, thus showing the absence of current. When the bar magnet was suddenly withdrawn from the helix, the galvanometer needle was again deflected, but now in the opposite direction, showing that the direction of the current in the helix had been reversed.

The preceding are but some of the results that Faraday obtained by means of his experimental researches in the direct production of electricity from magnetism. Let us now briefly examine just what he was doing, and the means whereby he obtained electric currents from magnetism. We will consider this question from the views of the present time, rather than from those of Faraday, although the difference between the two are in most respects immaterial.

Faraday knew that the s.p.a.ce or region around a magnet is permeated or traversed by what he called magnetic curves, or lines of magnetic force.

These lines are still called "lines of magnetic force," or by some "magnetic streamings" "magnetic flux," or simply "magnetism." They are invisible, though their presence is readily manifested by means of iron filings. They are present in every magnet, and although we do not know in what direction they move, yet in order to speak definitely about them, it is agreed to a.s.sume that they pa.s.s out of every magnet at its north-seeking pole (or the pole which would point to the magnetic north, were the magnet free to move as a needle), and, after having traversed the s.p.a.ce surrounding the magnet, reenter at its south-seeking pole, thus completing what is called the magnetic circuit. Any s.p.a.ce traversed by lines of magnetic force is called a magnetic field.

But it is not only a magnet that is thus surrounded by lines of magnetic force, or by ether streamings. The same is true of any conductor through which an electric current is flowing, and their presence may be shown by means of iron filings. If an active conductor--a conductor conveying an electric current, as, for example, a copper wire--be pa.s.sed vertically through a piece of card-board, or a gla.s.s plate, iron filings dusted on the card or plate will arrange themselves in concentric circles around the axis of the wire. It requires an expenditure of energy both to set up and to maintain these lines of force. It is the interaction of their lines of force that causes the attractions and repulsions in active movable conductors.

These lines of magnetic force act on magnetic needles like other lines of magnetic force and tend to set movable magnetic needles at right angles to the conducting wire.

The setting up of an electric current in a conducting wire is, therefore, equivalent to the setting up of concentric magnetic whirls around the axis of the wire, and anything that can do this will produce an electric current. For example, if an inactive conducting wire is moved through a magnetic field; it will have concentric circular whirls set up around it; or, in other words, it will have a current generated in it as a result of such motion. But to set up these whirls it is not enough that the conducting wire be moved along the lines of force in the field. In such a case no whirls are produced around the conductor. The conductor must be moved so as to cut or pa.s.s through the lines of magnetic force. Just what the mechanism is by means of which the cutting of the lines of force by the conductor produces the circular magnetic whirls around it, no man knows any more than he knows just what electricity is; but this much we do know,--that to produce the circular whirls or currents in a previously inactive conductor, the lines of force of some already existing magnetic field must be caused to pa.s.s through the conductor, and that the strength of the current so produced is proportional to the number of lines of magnetic force cut in a given time, say, per second; or, in other words, is directly proportional to the strength of the magnetic field, and to the velocity and length of the moving conductor.

Or, briefly recapitulating: Oersted showed that an electric current, pa.s.sed through a conducting circuit, sets up concentric circular whirls around its axis; that is, an electric current invariably produces magnetism; Faraday showed, that if the lines of magnetic force, or magnetism, be caused to cut or pa.s.s through an inactive conductor, concentric circular whirls will be set up around the conductor; that is, lines of magnetic force pa.s.sed across a conductor invariably set up an electric current in that conductor.

The wonderful completeness of Faraday's researches into the production of electricity from magnetism may be inferred from the fact that all the forms of magneto-electric induction known to-day--namely, self-induction, or the induction of an active circuit on itself; mutual induction, or the induction of an active circuit on a neighboring circuit; and electro-magnetic induction, and magneto-electric induction, or the induction produced in conductors through which the magnetic flux from electro and permanent magnets respectively is caused to pa.s.s--were discovered and investigated by him. Nor were these investigations carried on in the haphazard, blundering, groping manner that unfortunately too often characterizes the explorer in a strange country; on the contrary, they were singularly clear and direct, showing how complete the mastery the great investigator had over the subject he was studying. It is true that repeated failures frequently met him, but despite discouragements and disappointments he continued until he had entirely traversed the length and breadth of the unknown region he was the first to explore.

Let us now briefly examine Faraday's many remaining discoveries and inventions. Though none of these were equal to his great discovery, yet many were exceedingly valuable. Some were almost immediately utilized; some waited many years for utilization; and some have never yet been utilized. We must avoid, however, falling into the common mistake of holding in little esteem those parts of Faraday's work that did not immediately result either in the production of practical apparatus, or in valuable applications in the arts and sciences, or those which have not even yet proved fruitful. Some discoveries and devices are so far ahead of the times in which they are produced that several lifetimes often pa.s.s before the world is ready to utilize them. Like immature or unripe fruit, they are apt to die an untimely death, and it sometimes curiously happens that, several generations after their birth, a subsequent inventor or discoverer, in honest ignorance of their prior existence, offers them to the world as absolutely new. The times being ripe, they pa.s.s into immediate and extended public use, so that the later inventor is given all the credit of an original discovery, and the true first and original inventor remains unrecognized.

We will first examine Faraday's discovery of the relations existing between light and magnetism. Though the discovery has not as yet borne fruit in any direct practical application, yet it has proved of immense value from a theoretical standpoint. In this investigation Faraday proved that light-vibrations are rotated by the action of a magnetic field. He employed the light of an ordinary Argand lamp, and polarized it by reflection from a gla.s.s surface. He caused this polarized light to pa.s.s through a plate of heavy gla.s.s made from a boro-silicate of lead.

Under ordinary circ.u.mstances this substance exerted no unusual action on light, but when it was placed between the poles of a powerful electro-magnet, and the light was pa.s.sed through it in the same direction as the magnetic flux, the plane of polarization of the light was rotated in a certain direction.

Faraday discovered that other solid substances besides gla.s.s exert a similar action on a beam of polarized light. Even opaque solids like iron possess this property. Kerr has proved that a beam of light pa.s.sed through an extremely thin plate of highly magnetic iron has its plane of polarization slightly rotated. Faraday showed that the power of rotating a beam of polarized light is also possessed by some liquids. But what is most interesting, in both solids and liquids, is that the direction of the rotation of the light depends on the direction in which the magnetism is pa.s.sing, and can, therefore, be changed by changing the polarity of the electro-magnet.