We thrust one of the wires into the tube, then mixed equal parts of the silver and nickel filings and put as much of the mixture into the tube as we could hold upon the tip of a penknife blade, and then thrust in the other copper wire. (See Fig. 182.) The ends of the wire were about one eighth of an inch apart and the gap was loosely filled with the metal filings. This was connected by short pieces of copper wire, as shown in Fig. 183, to a dry battery cell, B, and a sensitive ammeter. When all connections were made the needle of the ammeter remained at zero, showing that no electric current was passing, that is, the battery cell was unable to send any electricity through the metal filings.

This is the apparatus which is to help us detect electric waves when they pass about us. Electricity has been called invisible light, that is, invisible to our eyes, and this apparatus has been called an "electric eye" because it will detect electric waves in the ether, just as our eyes may detect light waves passing through the ether.

We placed the automobile spark coil upon the table near to the tube containing the filings of silver and nickel, and as soon as we made a spark pass between the knobs the ammeter needle moved half way across the scale, indicating that the spark had somehow influenced the metal filings in the tube so that now they permitted the battery cell to send some electric current through them and through the ammeter. I asked one of the boys to tap the tube slightly with a lead pencil so as to jar the metal filings, and as soon as he did so the needle of the ammeter went back to zero.

The spark coil sent electric waves out in every direction, and those which hit the metal filings made them cohere together. In that condition they allowed the dry cell to send through them enough current to move the needle of the ammeter. Tapping the tube made the metal filings break apart again, in which condition they do not allow the current of the cell to pass in sufficient quantity to move the needle. This tube is called a coherer, because the filings in it cohere together. The apparatus then serves to indicate when electric waves are passing. As yet, however, it would not respond when the spark coil was more than one foot away. Our next step was to attach extra pieces of wire, each ten or twelve feet long, at either end of the coherer, as indicated in Fig. 184. One of these wires was stretched out upon the floor while the other one was connected with the wire of a picture hanging upon the wall.

We now found that the coherer would respond when the spark coil was operated several feet away. The extra wires which we had attached to the coherer are called antennæ, because they suggest the long "feelers" or antennæ of some insects.

Our next step was to put antennæ upon the spark coil also, as shown in Fig. 185. One of these wires was stretched out upon the floor, while the other one was connected with the wire of a picture hanging upon the wall on the opposite side of the room from where the coherer was. We now found that the coherer would respond when the spark coil was operated in the farthest part of the room. With the wires which were lying upon the floor extending toward each other, but lacking several feet of touching, the coherer responded when the spark coil was operated in various other rooms of the house, although the doors between were shut. When the floor wires were connected to the water pipes the coherer would respond when the spark coil was operated in a neighbouring house. We tried a similar experiment, substituting an ordinary electric bell for the spark coil. The coherer or electric eye detected that ether waves were sent forth from an electric bell every time a spark was produced in the bell. For this purpose connections were made, as shown in Fig. 186. One dry battery cell was used to ring the bell. The floor wire a, or, as it is usually called, the ground wire, was connected to the binding post 1, and the other antenna was connected to the screw 3, and then supported aloft on a picture hung upon the wall. With this transmitter we sent waves across the room which were detected by the coherer.

We constructed a simple spark coil as follows: We bought a pound of No. 24 single cotton covered copper wire, such as is used in the electro-magnets of bells. It was, when we bought it, wound upon a wooden spool. We filled the hole in the centre of this spool with wire nails. One dry cell was connected with this (Fig. 187). When the wires at d were touched together, and then separated, a spark was produced at that point. A ground wire was connected at b, and an antenna at c, as before. Using this apparatus now as a transmitter of ether waves, we found that the coherer detected them.

We next gave our attention to making changes in the receiving apparatus, not to change the coherer, but to provide substitutes for the ammeter. A sensitive relay was procured, which is essentially like a bell or buzzer except that it does not clatter. It will be readily understood, by referring to the accompanying Fig. 188, that R is a coil of insulated wire around an iron core exactly like what we see in the electric bell. (In practice there will be a pair instead of one of them.) Such coils are called electro-magnets, because when electricity flows in the wires they become magnets, and will attract iron. A is an iron spring, B is a dry battery cell and C is the coherer. Whenever an ether wave passes the coherer permits the battery cell to send a current around the magnet of the relay, and it attracts the iron spring a, so that it hits against the metal post d with a click. Whenever we used this to respond to ether waves the click of the relay suggested the telegraph sounder. How it served in wireless telegraphy will appear in the following pages.

XXII

RINGING BELLS AND LIGHTING LAMPS BY ELECTRIC WAVES

Harold was to have a birthday party, to which many of his school friends were invited. For this occasion he prepared, with my help, to perform for the girls and boys some electrical experiments, and particularly to give all who chose to try it an electric shock. For this purpose he had them all join hands, and the electric charge was sent through the whole line at once. One thing he did shocked his mother more than anything else. He instituted a mock court, at which one of the boys was tried, convicted and condemned to be executed by electricity. The whole affair was enacted with no great solemnity, but the electrical experiment was voted a great success by the executed "criminal." The following group of experiments, however, seemed to give the most satisfaction: On a table was placed the coherer connected to the relay, and in another room was placed the spark coil for sending ether waves. He had this operated by a confederate whom he chose for the purpose. He then connected two wires to the relay, one at d and the other at e (Fig. 189). These ran to a battery cell and a bell in a far corner of the room. At a given signal (a cough) the confederate made a spark at the spark coil in the other room; this sent ether waves through the partition between the rooms; the ether waves caused the coherer to pass electricity from the dry cell No. 1, to close the relay spring R. This acted like a switch to close the second circuit through the dry cell No. 2 and the bell, which rang out to the surprise of all. It continued to ring until he tapped the coherer tube and broke apart the filings. When this had been tried to the satisfaction of all, the company was invited to another room. Here they found an electric train with tracks, train sheds, stations, tunnels, bridges, switches, signals, etc., arranged upon a centre table. The electric train was to be started by ether waves. A wire from the railroad track was connected with e of the relay (See Fig. 190). A wire from d of the relay was connected to the third rail through a battery of sufficient strength (Battery 2). The electric train completed the circuit by connecting the tracks with the third rail. All heard the crack of the spark coil in the adjoining room, and saw the train start immediately. Ether waves had caused battery 1 to close the relay R. This had closed the circuit so that battery 2 might run the train, of course by means of a motor in the train. He tapped the coherer. The relay spring R flew open and the train stopped. Presently another crack from the adjoining room, and the train instantly started again. When all the details of the electric train had been examined the company was invited to go to the dining room, which was dimly lighted by candles. All were seated and busily conversing when the crackling noise of the spark coil was again heard, and a group of little electric lights flashed forth upon a birthday cake. The wires from the lamps and a battery to run them had been connected with the binding posts d and e of the relay.

The chandelier over the dining-room table had a pendant push button A (Fig. 191), with which the regular electric lights could be turned on and off. This I had removed and extended the wires down upon the table. It was only necessary to connect these to the binding posts d and e of the relay, and the next wave from the spark coil lighted the chandelier.

The flexible wires underneath the dining-room table with which the maid is usually summoned from the kitchen were next extended up and connected with d and e of the relay, and the maid was called in by an ether wave. She brought with her a tray in the centre of which stood an earthenware cup, such as is used for baking custard. This had been filled with a mixture of granulated sugar and powdered potassium chlorate. Four dry battery cells stood around this upon the tray connected in series (Fig. 192). A very small iron wire connecting two of these cells dipped into the sugar mixture. Two wires from the battery were connected to d and e of the relay. At the proper signal an ether wave was sent out by the spark coil. The coherer closed the relay and the relay acted as a push button to close the circuit of the four cells upon the tray. The fine wire dipping into the sugar and potassium chlorate got red hot. This caused the mixture to flash up and burn in most beautiful coloured flames. (Fig. 193).

XXIII

TELEGRAPHING BY ELECTRIC WAVES

The next time Harold and I experimented we arranged something to save us the trouble of tapping the coherer each time we used it. We employed simply an electric bell, B (Fig. 194), from which we removed the gong. By reference to the figure the arrangement will be understood. Each time ether waves cause the metal filings to cohere and the battery B¹ closes the relay R, battery B² causes the hammer of B³ to tap against the coherer. This causes the current to cease to flow from B¹ and the relay opens again by its own spring.

Our next addition was a telegraph sounder as shown in Fig. 195. B¹ is a single dry cell, C is the coherer, R is the relay, B² is now a battery of three cells. Part of its current goes to B³, the tapper for the coherer, and part of its current goes to the electro-magnet of the telegraph sounder S. Ordinarily a spring holds the iron strip d up against the metal stop a, but when the current passes through the electro-magnet it pulls down this iron strip with a click against the metal stop e. But while this is happening C is being tapped by B, and is ready to respond to each wave. It was only necessary now to have some code of signals in order to communicate by telegrams. We learned the system of dots and dashes, or short and long periods marked off by the sounder, which all telegraphers use and which is known as the Morse alphabet, and very soon Harold and I were telegraphing from one room to another messages of several sentences at a time, the Morse alphabet being told off on the spark coil and being received through the coherer and telegraph sounder. It was not long before Harold and one of the neighbours' boys were exchanging messages between their homes, each having a spark coil and the necessary receiving apparatus, and having extended their antennæ to the top of the buildings into what are called in the wireless language aerials.

The fever for wireless telegraphy spread like wild-fire among the boys. In a few months they had formed a "wireless club." They had each read anywhere from ten to thirty books and articles upon the subject, and had secured the latest improved apparatus. They made it a practice to spend hours daily at their instruments picking up and keeping on file messages which were sent to and from steamers leaving the harbour for European ports. On one occasion they showed me from these files scores of messages—fond, personal, and supposedly private farewells to friends and communications between business partners which they would never have made on land without first closing the office door. The boys had acquired a mass of technical knowledge upon the subject which far exceeded my comprehension. But their teachers in school complained that they would learn nothing else, and some of the boys had already received warning that they might fail of promotion.

How to have compelling interests without riding hobbies is the great problem for both boys and men. I have known many boys who could, or at least would, do nothing well in school or out, except some specialty like manual training or science. In later years they were so deficient in education that they could hold no worthy position in anything. My anxiety was to save my boy from such a fate. I was determined that he should have a fair share of all kinds of culture. To this end we read together much of biography, history and classical literature, ancient and modern, through the medium of the English language.

As both prevention and cure of the wireless telegraph mania I deemed it not necessary to suppress enthusiasm, nor to introduce obviously useless tasks for the sake of the training which might be in them. My method was, on the contrary, to encourage my boy to have several hobbies which he might ride with enthusiasm, but to make it a rigorous rule to exchange his "mount" occasionally.

XXIV

HALLEY'S COMET AND ELECTRICAL WAVES

"Although Halley's comet has come within the earth's orbit about three thousand times since its first recorded appearance, I know of no man living who can give a satisfactory account of having seen it. Any one who has seen it before must be at least seventy-five years old, for it requires seventy-five years to make one complete circuit of its own orbit. But no one who is now seventy-five could have observed it intelligently, and even one who is now eighty-five years old would have to tell what he saw when he was ten years old and has remembered for seventy-five years. Furthermore, any account of how it looked on a former return is no guide to how it may appear on this trip. You may properly think of the comet as a group of solid pieces no bigger than the stones you may throw, scattered, two or three to the mile, through a space 12,500 miles broad. This extremely thin cloud of particles does not reflect enough sunlight to be visible, even in a telescope, in any part of its journey, and hence we should be wholly unaware of its existence if it did not sometimes have the strange faculty of giving out light of its own while in that part of its own orbit nearest to the sun. At such a time there is a hazy light enveloping the mass of small bodies, and streaming away sometimes many million miles from them. The mass of small bodies is generally referred to as the nucleus, and the stream of luminous gas which the nucleus gives forth is called the tail, though it reminds me more of a search-light.

"It does not trail along behind the comet but always points away from the sun (Fig. 197). The normal thing for a comet to do is to begin to develop a faint light and a short streamer as it gets near to the sun, to have its light grow brighter and its streamer to grow longer until it reaches the point nearest the sun, and then to have its light grow dimmer and the streamer grow shorter as it recedes from the sun.

"It has many times been suggested that this strange search-light appearance may be an electrical phenomenon, some form of ether waves which the comet sends forth when under the immediate influence of the sun. But not all comets are alike in this matter, nor does the same comet always act alike on succeeding trips, so that we may not predict what Halley's comet will do on this visit. It would be natural to suppose that Halley's comet, like radium, might in time lose the power to radiate off material, in which case it might at length become wholly invisible to us, even though it continued to travel in its wonted path. Our only way of knowing of its existence then would be that on its returns some of its small pieces might be attracted to the earth and enter our atmosphere as meteors. This sort of thing is continually happening, and may be the last reminders of once brilliant comets.

"For almost a century it has been the common belief that light is merely a wave motion in the ether. Our eyes respond to ether waves of certain length only. Waves a little longer than those which affect our eyes are felt by us as heat waves. Waves still longer than those of heat are the so-called electric waves. These we use in wireless telegraphy. There are still shorter waves than those of light. These affect the sensitive plate in photography. They help to form the green material in the leaves of plants and the brilliant colours in flowers. They assist in the fading of our clothes and the tanning of our skin. These are called chemical waves. Still shorter waves in the ether than those of which we have just spoken are the X rays, and all the strange things which they may do have not yet been determined. Certain it is that they can make dreadful sores in our flesh. They can penetrate through wood and paper, but not metals. They pass readily through flesh, but not bones. All such ether waves are treated in a book by Sylvanus P. Thompson, entitled 'Light Visible and Invisible,' in which he points out that electricity, heat, light, chemical rays, etc., are all alike in being ether waves, and this was suspected by James Clerk Maxwell and others half a century ago, and has come now to be quite generally believed.

"Halley's comet, already having been seen upon this return, must be sending out those ether waves which we call light; whether it is also sending forth some of the other kinds of ether waves may yet be determined."

My audience being chiefly composed of those persons who were present at Harold's birthday party, they pressed me to tell them more about wireless telegraphy and similar matters, and so I agreed to give them at some future date some account of the history of these ideas. But my present purpose was to start an interest in astronomy as an antidote for the wireless epidemic, and so I invited all who desired to do so to come again one week from that evening, bringing with them such opera and field glasses as they might be able to secure. I promised to show them how to make a telescope such as Galileo had more than three hundred years ago. I agreed to go out with them several evenings and scan the sky with our telescopes, and to tell them of some readable books and articles upon astronomical matters.

XXV

HOW THE IDEA OF A UNIVERSAL ETHER DEVELOPED

The evening for the meeting of the Science Club had arrived. Its membership had increased tenfold within a year. At its monthly meetings, which were open to the public, an audience of two hundred, old and young, was usually present—a number about three times that of the regular membership. General science was now the study of this club. At its weekly meetings, which only members attended, the studies of specific topics by individuals, oftentimes illustrated by experiments, were reported. These meetings were held in one of my laboratories, while the open monthly meeting was always held in my lecture room, with some rather famous speakers to instruct the audience. An enthusiastic friend of science had given a fund with the stipulation that we should engage the services of those who both knew their subjects and had acquired the art of presentation. The fund was $10,000 and it yielded $500 a year. I think beyond question it was doing more for science than any other fund of ten times that amount which can be mentioned.

On the particular evening of which I am about to speak, the lecturer told the members of the Science Club frankly how, beginning at the age of thirteen, he had spent forty years of enjoyment in study, that he had always found great satisfaction in the study of ancient civilizations and literatures. He had been fortunate, he said, in having teachers early in life who could make these subjects full of meaning to him. His greatest satisfaction, however, during the last twenty-five years had been found in tracing the development of modern science, both in the evolution of its theories and in its applications to modern industries. He said he was sure that young people of high-school age would find it profitable to learn, for instance, how the modern theory of combustion had developed slowly through the centuries, even if to do so they must curtail somewhat their study of how Greece and Rome developed and declined. He said that science furnished a tremendously rich field of study for young people, which as yet had been untouched by our schools, first, because educational conservatism had made it impossible to determine the relative importance of subjects of study, and, second, because education in science had, for a brief period, found its worst enemies within its own camp. He would like especially to commend on this evening some historical studies in science, and had chosen for his subject, "How the Idea of a Universal Ether Developed."

Men seem to talk freely now about the transmission of light, heat, and electricity by means of the ether. How did this idea arise? Is it a product of wild imagination? or did the idea develop out of experiences which, if given to any person of fair intelligence, would yield the same result?

A little over thirty years ago, at the Royal Institution of Great Britain, James Clerk Maxwell (1831–1879) delivered a lecture on "Action at a Distance." It was no new subject, but rather one of the oldest and most often discussed subjects from the days of the ancient Greeks down to the present. We talk of gravitation as an attraction or pull between the various bodies of the universe, but how can they pull one another without some material bond between? This was Sir Isaac Newton's great puzzle which he never solved, though he expended upon it the greatest efforts of his great intellect.

The sun appears to repel the tail of the comet, yet how can there be a push without intervening material with which to push? When we speak of light pouring or streaming in, do we think of it as a substance? When we speak of warm bodies losing heat, or when we cover them to keep the heat in, are we thinking of heat as a substance? What are heat, light, electricity, magnetism, and gravitation?

These are no new questions. They are certainly older than history. Various ideas have prevailed at different times. It is much easier to change our ideas than to change our language. You occasionally see and hear the words calorie and caloric used in connection with heat. They stand for an idea, abandoned for three generations, that heat is a substance called caloric, which saturates warm bodies and drains out of them when they cool off. I hardly think these ideas either arise or fall without good and sufficient reason. Each theory has been the natural conclusion from our observations of nature as far as we have gone with them. To be sure, it is difficult for us to see how men acquired, from any observations of nature, the idea of light which seems to have prevailed previous to the time of Aristotle, three and a half centuries B.C. This idea was that objects were made visible by something projected from the eye itself. Still, the questions which I have indicated regarding heat, light, and electricity have impelled men for many centuries to observe nature for hints as to the answers. The doctrine of the universal ether as a medium for transmitting wave motions, and of light, heat, and electricity as being motions of different wave length, is the natural conclusion of the present time. It may give place to another theory when we have further facts to reason upon. Imagine your never having seen a harp or other musical instrument. Would it require a long time, do you think, for you to find out its use, at least to this extent, that it will produce tones whenever the strings are made to vibrate? That the short strings vibrate more rapidly than the long ones, and at the same time produce tones of a higher pitch? Imagine that having become familiar with the harp you should successively come upon scores of other musical instruments of very differing types. You would soon become adept at divining their uses. Now, a study of the microscopic structure of the eye, for one thing, would suggest that light may be in the nature of a vibration. Scores of other lines of study in a similar manner have at length brought all who pursue them to the conclusion that light is a form of vibration.

Robert Hooke in England (1631–1703) and Christian Huygens in Holland (1629–1695), back in the seventeenth century seem to have been the first to give expression to this idea, which was nothing more than an inkling in Hooke's mind, but which was the necessary result of observations on the part of Huygens. For nearly a century the idea lay dormant, largely because Sir Isaac Newton (1642–1727), the cleverest thinker of his time, opposed it. It was perhaps unfortunate for the success of the theory that Huygens, its founder, adopted the word ether, for that was an old term, and had been very badly overworked. The word ether, or æther as it was often written, had been invented in the days of ignorance, for such foolish reasons as: (a) because "nature abhors a vacuum," or (b) "for planets to swim in," or (c) "to constitute electric atmospheres and magnetic effluvia," or (d) "to convey sensations from one part of our bodies to another."

"When we remember," says Maxwell, "the mischievous influence on science which hypotheses about æthers used formerly to exercise, we can appreciate the horror of æthers which sober-minded men had during the eighteenth century."

Newton in England (1642–1727) and Laplace in France (1749–1827) stoutly opposed the undulatory theory of Huygens and championed a corpuscular or emission theory, that light-giving and heat-giving bodies emit a subtile fluid.

There is no other instance in the whole history of modern physics in which truth was so long kept down by authority. Fresnel (1788–1827) and Arago (1786–1853) in France appear to be the only persons during the eighteenth century who caught a clear vision of the truth of the undulatory theory.

But it remained for Mr. Thomas Young (1773–1829), a colleague of Sir Humphrey Davy at the Royal Institution, in his Bakerian lecture (1801) on "Theory of Light and Colour" to bring together such good evidence for the ether wave theory that it has hardly been questioned since.

Young, like Davy, was a most remarkable man in literature and in science. It was he who first deciphered the Rosetta Stone, now in the British Museum, and gave us a key to the Egyptian hieroglyphics. Probably he was the only man who was able to overthrow the influence of Newton's authority even a century after Newton did his work.

Faraday's (1791–1867) chief work as director of the laboratory of the Royal Institution, London, was a study of ether phenomena, particularly electric and magnetic. About seventy-five years ago he became impressed with the fact that although wires may give direction to an electric current the electric influence is not confined to the wires, but may permeate more or less widely the region about them.

Nearly fifty years ago Maxwell (1831–1878) professor of physics at Cambridge University, England, conceived the idea that light is electricity of a very short wave length.

Nearly twenty-five years ago Heinrich Hertz (1857–1894), in Germany, proved by experiments the existence of electric waves, and measured their length and velocity, determining their various characteristics as compared with light.

About fifteen years ago Marconi developed a wireless telegraph apparatus, which made it possible to use electric waves for purposes of communication.

Thirteen years ago (1897) the first wireless telegraph company was formed. Eleven years ago (1899) the international yacht races in New York Harbour were reported by wireless telegraph, and bulletin boards in New York City announced to waiting crowds the details of the race while it was in progress. Nearly ten years ago (1901) wireless despatches were first sent across the Atlantic Ocean. Wireless telegraphy was opened for public use in 1905, and very soon the company began to coöperate with the regular telegraph companies. Nearly all coastwise and trans-Atlantic steamers are now equipped with wireless telegraph outfits, and a law has passed both houses of Congress making it obligatory on the part of steamers which carry fifty or more passengers to have such equipment. On several disabled steamers, notably the Republic, loss of life has been averted by the wireless emergency call for help, to which the captains of all steamers feel obliged to respond. If you desire to communicate with a friend who left for Europe several days ago, you simply write him a telegram, addressing it to his ship, and deliver it at your nearest telegraph office. Each telegraph office has a record of the location of every ship having a wireless telegraph outfit. It despatches your message to the wireless station along the coast which is nearest to your friend's steamer, and from this station it is sent on the ether to the ship. Or in some cases it may be repeated from one ship to another along the Atlantic highway until it reaches the desired one. Thus also news of important events on either continent is distributed daily on board ships which are crossing the ocean. There are said to be more than 50,000 amateur wireless stations in the United States, and already Congress is taking steps to regulate the use of the wireless telegraph in order to prevent interference with Government and other important messages.

More than three dozen books and countless magazine articles have already been written upon wireless or ether wave telegraphy. Hundreds have and thousands are contributing to our knowledge of ether wave phenomena. If the names of all who have said or done something to render stable the foundations of this idea of a universal ether, whose undulations account for the phenomena of heat, light, and electricity, were to be mentioned, the list would contain nearly all the important workers in the field of physics for the last century.

XXVI

ELECTRIC CURRENTS CANNOT BE CONFINED TO WIRES

In my first experiment on that occasion I took a one-pound spool of No. 24 cotton-covered copper wire and crowded the hole in the spool full of wire nails A (Fig. 198). I disconnected the wires from an electric drop lamp and connected them to b and c, the ends of the wire from the spool. Our electric lighting circuit was what is called the alternating current. I also had a second spool, B, precisely like the first. The wires from this were connected to a miniature lamp, L, such as is used at the switchboard of a telephone exchange. We then screwed the drop-light plug into the chandelier and turned on the electric current. I brought spool B with the miniature lamp near to spool A, as shown in Fig. 199, and when it was within a distance of about two inches the little lamp lighted up to full brilliancy, thus showing that while the electric current is passing in the wire of spool A its influence is not confined to the wire, but exhibits itself in the region outside of the wire. To illustrate still further this fact we substituted an electric bell in the place of the lamp L, and when the spool B was brought near to A the bell rang. But the most striking illustration was obtained when a telephone receiver was put in the place of L. With this held to the ear while the spool B was brought toward A a humming sound could be heard when B was about a foot distant from A. This sound grew rapidly louder as B approached A, until, when the spool B rested upon the spool A, a sound like the peal of a pipe organ was heard all over the apartment. The tone was very nearly that of the key on the piano which is two octaves below middle C. I unscrewed the cap on the large end of the telephone receiver, took it off, and moved the thin iron diaphragm to one side, when it began to dance about at great speed. It was keeping time with the dynamo, five miles away, which generated the electric current. The dynamo changed the direction of the electric current sixty times per second, and this made sixty vibrations per second. The dynamo sent out ether waves which affected the telephone receiver, although the receiver was not connected to the dynamo by wires.

To emphasize the fact that the dynamo had lighted the lamp, rung the bell and made the telephone receiver hum without being connected with them, I repeated all these experiments in a different way. Spool A, connected as before with the electric lighting circuit, was concealed beneath the table. For spool B I substituted spool C (Fig. 199), on which the wire was wound so as to appear like a candlestick. On the top of this was placed the miniature electric lamp screwed into a miniature socket and connected to the wires of the spool. This "Witches' Candle," as we called it, was sitting unlighted upon the table when I called attention to the fact that if I moved it to a certain spot upon the table it flashed into full light. (Of course this spot was directly over spool A.) I moved it slowly away from that spot and its light slowly grew dim and disappeared.

On the table was also sitting a cream pitcher in which I had placed spool B with a buzzer attached to it. Remarking that this pitcher groaned for more cream whenever it was empty, and thus of its own accord called the waiter, I moved it to the spot on the table directly over spool A, when the buzzer gave forth a sound like a husky bumble-bee shut up in a resounding bottle. At this signal my assistant came in and took up the pitcher and placed my silk hat upon the table, when it instantly boomed forth a base note two octaves below middle C of the piano. Out of the hat I took a coil and the telephone receiver and the mystery was solved.

In 1819 Hans Christian Oersted in Denmark (1777–1851) first noted that the region about a wire carrying an electric current has an influence upon a magnet. I will show this fact by a simple experiment. I magnetize a stout sewing needle by drawing it from end to end across the pole of a steel magnet, and by means of a triangular piece of paper and a fine thread I suspend it a few inches above the table (Fig. 200). I then lay upon the table a piece of wire parallel with the needle and fasten one end of it to one binding post of a dry cell. Whenever I touch the other end of the wire to the other binding post of the cell, thus sending an electric current through the wire, the magnetized needle is deflected at right angles.

This experiment, performed by Oersted, seems to have started Faraday upon that wonderful series of researches which has resulted in giving us the dynamo.

XXVII

WIRELESS TELEGRAPHY IN EARNEST