Popular Science Monthly/Volume 20/March 1882/Recent Wonders of Electricity I
By W. H. PREECE, F. R. S.
I OUGHT to commence, if I carried out the customary practice, by addressing the audience as ladies and gentlemen, but to-night I much prefer commencing with boys and girls, because the two lectures that I am about to deliver to you are really intended to be addressed to the youngest members of the society. I would first direct your attention to the fact that this hall is illuminated by electricity, and, although I do not intend in any way to refer to the electric light to-night, it is my intention, step by step, to lead you up to it, so that, when we part this day week, I hope and trust to be able to let you depart with a thorough and complete knowledge how electricity works and how it produces these marvelous effects. To accomplish this object there are two things most essential: the first is, that I, your lecturer, should be perfectly clear in my definitions, and simple in the language I use; the second is, that you should devote to me your very earnest and best attention, and strive all you can, by thought afterward, to understand what I mean. I shall use, doubtless, unconsciously, a great many words that are new to you, but which are to me just as familiar as household words. I will, however, try to explain them, and endeavor, if I can, to let those words impart to you the very idea that they conjure up in my mind. At the commencement, there are two words in very common use that many of you have heard over and over again, but which convey, in the way I shall use them, perhaps a different conception. These two words are "work "and "energy." I can readily imagine that one of you boys may say, when I call your attention to the words "work" and "energy," "Why, what nonsense to talk to me about work! Have I not been working as hard as ever I can during the past term to gain a prize, and have not I exercised all the energy I possess to distinguish myself in my class?" But the words "work" and "energy" applied in that sense are applied in a mental sense, and not at all in the physical sense in which I shall use them. Now, I dare say many of you live in town; some may live in the country; but, whether you live in town or country, you all know what a garden is, and what a gardener does. Suppose a gardener, with a ton of gravel in front of him, were told to move that gravel to a height of three feet. He would go to work with his spade; he would move shovelful after shovelful from the ground-line up to the three feet height, and after he had moved the whole of it you might readily imagine that he would be a little fatigued. Now, whenever a person does anything which causes fatigue, he does what we call work. The gardener, in lifting the gravel, would perform an amount of work which is capable of being measured. I will give you another illustration. Supposing some of you boys were put beside a pile of cricket balls, and for a wager or prize you were called upon to throw the balls as fast and as far as you could. A good thrower would perhaps throw the first ball eighty yards, he would throw the second ball seventy-five yards, the third seventy yards, the fourth sixty-five yards, and so each ball that he threw would go a less and less distance, until he had no strength left, and he could throw no more balls. Now, that boy would have done work; something would have passed out of him into the balls; he has, as it were, passed something that belonged to him into the cricket-balls, and as a result he feels fatigue through the loss of this something. Take another illustration: Supposing two crews agree to row a race. They start full of life and full of energy; they pull with all their hearts and might, and arrive at the goal, in common language, thoroughly pumped out. Something has gone out of them into the boat. That which has gone out of the crew, and out of the boy who threw the cricket-balls, is what we call energy, and what they have done is to do work upon the boat. Another example is in the case of foot-ball. A boy kicks a foot-ball and makes a splendid goal. To do that he has sent something out of his body into the ball which hurtles through the air past the goal, and the game is won. In all these illustrations something is done which results in fatigue, work is performed and energy is lost; in fact, work done means energy applied, and energy applied means work done. As mental energy is our capacity for learning lessons, for going through examinations, and that kind of thing, so the energy of the kind I speak of is the capacity for doing absolute physical work. The generality of this energy is immense. It is a difficult thing to grasp the fact that there is something in existence that we can not feel, that we can not touch, and that we can not see, but which gives us all the force and all the power we possess. The earth as it moves around the sun and the earth as it daily rotates upon its own axis are instances of the existence of this energy; in fact, every kind of change produced in the condition of matter, whether it be in its physical state or in its position with reference to fixed objects, means energy gained or energy lost. The energy gained or lost is the quantity of work done on a body, or done by that body; so I want you to grasp, if you possibly can, the fact that every case of motion on this earth—even the sound of my voice, as I now speak to you—is due to the exercise of this particular energy. Lecturing, for instance, is a considerable exercise of energy. A man can lecture pretty well for an hour; he can lecture not quite so well for two hours, but the best lecturer in the world can scarcely keep at it for three hours without losing all his energy, and, like the crew in the boat, being thoroughly pumped out. This energy—or work done, as I have said—is measurable. The gardener who moves his ton of gravel three feet high has done an amount of work that any boy can calculate who will reduce one ton to pounds, and multiply that sum by three. He will then have obtained 6,720 what we call foot-pounds. One pound raised one foot high is the common and ordinary unit of work; 33,000 pounds moved one foot high is called a horse-power, and the horsepower is the mode by which the power of steam-engines is measured. One steam-engine is known from another by its being able to exercise ten, twenty, or fifty horse-power; and so, whether it is merely the lifting of gravel—or a small tube, such as I have here—throwing a cricket-ball, moving a boat, or working a steam-engine, it can all be measured by this simple unit of foot-pounds. Two other terms are necessary in order to make you comprehend what energy is. Energy is found in two conditions—called "potential" from its position, and "kinetic" from its motion. The potential form of energy is that which exists in the form of a wound-up watch-spring: you wind up the spring of your watch, and by doing so you pass something from your body into it—you transfer energy from your own body into the watch, the spring is wound up, and the watch thereby can be kept going for twenty-four hours or more from the storage of energy imparted to it. A clock, again, will go for eight or fourteen days by your winding up the weight until you impart to the clock energy in this potential form of sufficient power to keep a clock going for a fortnight. In gunpowder there exists a splendid example of the storage of energy. It remains quiescent until heat is applied, when its potential form of energy is at once transformed into its active or kinetic form, impelling a cannon-ball or bullet with tremendous force. Coal, again, is a grand store of energy. All our steam-engines employed in manufactures are set going by the energy that is stored up in coal. This energy has remained stored up in coal for millions of years in the bowels of the earth, it is brought to the surface, and is there used to produce power in the innumerable ways with which you are acquainted. Take food—I had a very good chop just now that supplied me with a store of energy which will enable me, for one hour at least, to talk to you; and, had I not had that chop, I do not think I could have talked to you for more than half an hour, instead of the three quarters more that I hope I may yet be able to get through. I have given instances of energy in its potential form. We will now take one or two instances of it in its kinetic form—that is, when it is in a state of motion. A moving cricket-ball is a good example of kinetic energy. In its passage through the air it possesses kinetic energy, and should the ball catch your head you know pretty well what is the effect. A steamship moving and a running railway-train are kept in motion by the energy imparted to them from coal, and we know what tremendous energy a steamship or a railway-train has, as when a collision occurs there is a terrific smash-up. Our earth is another magnificent store of energy in its rotation every twenty-four hours; a portion of this energy it gives up in the shape of tides. Our tides abstract energy from the earth, which is gradually robbing the earth of its motion, and the result is that our day is getting longer and longer. If any of you live a million years, you will probably find that the day will be a minute longer than it is now!
Such being the two general forms of energy, I want next to give you two or three ideas of the forms in which this mysterious energy appears. I had intended to bring a familiar toy, a humming-top, before you, to show you the energy it contained when spinning: but we have other illustrations of various kinds. Take a piece of a very dangerous material called sodium, a beautiful white metal, of which I have a quantity in a bottle here, put it on a piece of blotting-paper, and then place it on top of the water contained in this glass vase: you will see that the sodium possesses energy in itself in a potential form. The moment it is brought in contact with the water, the oxygen of the water unites with the sodium and produces the effects of heat, light, and sound, the result of the chemical energy of the sodium in its potential form being brought into the active or kinetic form by mere contact with the water. Another instance: Here is the dome of a bell, which I strike with a mallet or hammer, and thereby impart energy to it, and it sets the whole air of this room in motion, and every tympanum of every ear present is struck by the little bullets of air that are thrown into vibration, and the result is the effect called sound. As another illustration, I will take coal. I take a small piece of coal and warm it in an iron cup, so as to cause it to give out a little kinetic energy in the shape of heat, and, on placing it in this jar of oxygen [experiment performed], you see that the mere insertion of coal, slightly heated, in an atmosphere of oxygen, produces a most brilliant effect, which is the result of the conversion of the potential energy existing in the carbon, or coal, into the kinetic energy seen in the shape of motion, heat, and light. We have even more brilliant effect of this conversion of potential into kinetic energy. Here is a piece of magnesium wire which, when heated [light applied], has its potential energy converted into kinetic energy, and a most brilliant light is the result. But we need not go to light, and we need not go to heat, for instances of energy. I have shown you that energy is a form of motion; that it is so found in sound, heat, and light; but we also have energy as magnetism. There is a little toy-duck floating on the basin of water before me, and I merely hold in front of it a magnet, when you will see that a sort of affection is set up between the duck and the magnet, by the duck following the motion of the magnet round the basin. That is another form of energy. The last form of energy that I wish to draw your special attention to is that due to electricity. You have all seen the vivid flashes of lightning and have heard the dreadful roar of thunder; in those two effects we have energy. It is in its potential form when it exists in a charged cloud, and in its kinetic form when that charged cloud gives its charge up to the earth, and in flying to the earth produces that dreadful effect that we call lightning, with its accompaniment, the roar of thunder. Thus, you have illustrations of energy in its different forms, electrical, magnetical, chemical, heat, light, and motion.
Now comes the question, How is this energy transferred from place to place? You may have all stood upon the sea-beach and have seen the waves dashing upon the rocks, and sent up in the air in white and brilliant spray. You have seen the waves rolling over and over again in glorious breakers upon the sands. You have probably seen wrecks dashed to pieces by the force of waves, all which effects are the result of energy which has been imparted to the water by a storm miles and miles away, the energy of that storm having been transferred by the waves of the water till it meets with the resistance of the shore and produces those effects I have mentioned. Again, energy is transferred by air-vibrations. The explosion of a gun can be heard to a distance of twenty to twenty-five miles; and instances are known where the bombardment of a town has been heard at a distance of one hundred miles. It is well known that the roar of the cannon at Waterloo was heard on the English coasts, at a distance of over one hundred miles. Again, we have energy transferred from the sun to the earth by that thin, almost immaterial, subtile medium called the ether, by means of which we have motion transferred from the sun to the earth, which gives us at one moment light, at another moment heat, and at a third moment those effects that result in photographs. Energy is also transferred through matter in the shape of heat. I touch the lamps before me and feel them warm because the heat of the incandescent material which they contain has thrown the molecules of the covering glass into vibration, and that vibration imparts a vibration to my hand that gives the sensation of heat; and if I were to put a poker in the fire—which, no doubt, all of you have done—it would be found in a very short time that the heat of the fire had been transferred through the poker to your hand. Electric currents are a form of energy which is driven through matter. Electricity is transferred, principally, through metals; some of them transfer it with great alacrity—for instance, silver and copper. There are, on the other hand, materials, such as dry wood, glass, gutta-percha, India-rubber, and such like, that scarcely will allow any electrical energy whatever to pass through them; and the result is that bodies are divided into two classes, the one called conductors, that conduct electricity away, and the other called insulators, which prevent electricity from being conducted away. If you have noticed the telegraph-wires passing through the country, you will have seen that they are suspended on little earthenware knobs (there are specimens of the various kinds in use on the table for inspection), which are employed because they resist the passage of the electrical energy through them, and consequently the electrical energy must flow through the wire which they suspend to the distant end, where it is wanted to do work and produce desired effects.
We have now to consider the motive agency. I ought to have said at the first starting, as every boy fresh from school will know, ex nihilo nihil fit, from nothing nothing is created, and therefore there can be no effect without its cause There can be no wind without a difference of pressure in the atmosphere to cause motion of the air. At the present moment I can feel a draught, which is due to a higher pressure above and a lower pressure below on the other side of the door, and the air is circulating over my head from the higher to the lower pressure. The chimney-draughts are produced in a similar manner. Why are meteorologists able to tell us that there is a gale coming? Because they know that there is a higher pressure at one spot than there is on another; and where there is a difference of pressure there must be motion of air. So with water at different levels. The tendency is to produce a common level, and the passage of water from the higher to the lower level produces motion and energy. Tides are simply the result of the effort to produce equilibrium in the sea after it has been attracted in different directions by the force of the sun or the moon. Rivers flow because the water high up in the mountains is at a higher level than the ocean, and the purpose of their flowing is to produce equilibrium, or an equality of level. Heat circulates in our rooms because a higher temperature exists in the fire than in the walls. In the electric lamps before me there is a very high temperature, because the carbon is maintained in a very high state of incandescence, and on the approach of my hand, which is of a lower temperature, toward the lamp, instantly there is a passage of heat from the high to the low temperature, and I feel that heat striking my hand exactly in the same way that I feel the draught (before mentioned) on my shoulders. Lastly, take electricity. We can not speak of the level of electricity; we can not speak of the pressure of electricity, in the same sense that we can speak of the pressure of liquids. We can not speak of the temperature of electricity; but there is a peculiar condition of electricity analogous to all three, analogous to pressure, temperature, and level, and that peculiar quality or condition is called potential. When we speak of electricity of a high potential, it has exactly the same meaning as high level of water, or of high temperature, and wherever two differences of potential are produced, separated by a conductor, electricity flows. Having said so much, perhaps too much, I want to speak to you about the production of electricity. Having shown you the various forms of energy, how it is transferred, and why it is transferred, I want now to say something of the production of electricity. You know very well that a lump of coal is a store of energy; that is evident by placing it in the fire. There are certain contrivances by which electricity can be produced from coal, but the effects are difficult to show to an audience. So we will take zinc, which, for the purpose, is better than coal. Zinc is a grand store of energy in its potential form. Here is a piece which I take up and place in a glass jar, and in that same glass jar I put a piece of carbon. I then place water in the jar, and, if I added to the water a little sulphuric acid, I should produce a galvanic battery; there would be a difference of potential, of which I just spoke, between the zinc and the carbon, which leads to the production of a current of electricity when the zinc and carbon are joined by a conductor. I have forty of these cells, or a battery, down-stairs, and I have two wires connected with its two ends, now in my hands. I know my battery is all right because, you see, when I bring the ends of the wire into contact with each other sparks are produced, which show that electricity is passing. I will not explain those sparks to you to-day, because I wish to talk to you about electromagnetic effects of electricity and how they are utilized. The first is the production of magnetism. I have here an electro-magnet, which is simply a bar of iron enveloped by an insulated copper wire, and a poker. A poker can be utilized for a great many purposes, but my present purpose is to place it on the large electro-magnet before you. So long as the battery wires are not joined to the wire around the electro-magnet, and, consequently, no current is passing, you see that I can raise the poker from its position without difficulty; but, now I join on the wires connected with the battery to the coil of the electromagnet, the poker is attracted with greater force than my strength can overcome. The effect is more perceptible by the use of nails instead of the poker. When the current is on you see that, owing to the attraction of the nails by the magnet, I am able to build up an ornamental triumphal arch of nails, but, directly I take off the current, the magnetism ceases, and the nails succumb to the force of gravity, and fall to the floor. I have here the parts of an electro-magnet disjointed, which I will put together to illustrate the utility of this power of attraction. I place the iron bar surrounded with wire on the table, and, on holding nails to it, you see it possesses no attractive power. If I let the current pass from the battery through the coil, the iron is magnetized, the attractive action is immediately set up, and the nails are attracted. Now, suppose I want to utilize this power to ring this bell—the dome which I struck a short time ago—I place the hammer (which is attached to a piece of iron in position to be attracted similar to the nails, so as to imitate the motion of my wrist) in front of the electro-magnet; I then place the bell-dome on its rod, so that the hammer, when drawn forward, will fall upon it; and, as you will see, the arrangement is complete in that simple form, for each time a current is sent the iron armature is attracted by the magnet bringing with it the hammer which strikes the bell by its forward motion. This is the principle on which all electric bells are constructed. A similar arrangement is employed for giving alarms in case of burglary. A small switch arrangement is attached to the frame-work of the bedroom-door [a small door so fitted was exhibited]; this switch is put on on going to bed, and, should the door be opened by any one during the night, a succession of currents of electricity are sent to a bell, which continues to ring till attended to, and it would be a bold burglar who dared to carry on his nefarious business under such a din. A modification of this arrangement can be adapted to innumerable purposes. In America, where servants are not so plentiful as in England, necessity has compelled the employment of electricity for domestic purposes, to a far greater extent than in England. In nearly every town in America, systems of wires extend to almost every house, in the hall of which is a small instrument [one was exhibited], on the dial of which divisions bear the various words—messenger, carriage, coupé, express-wagon, doctor, police, fire, and two or three other things, and on turning the instrument pointer to any division, and drawing down a spring, a call is sent to the central office or bureau, and the instrument there indicates the service required and at what house, and the request is carried out at once. While traveling in America, I was once afraid that I should not have time to reach the nearest telegraph-office, to dispatch a telegram in reference to an appointment; and, on mentioning my concern to the lady in whose house I happened to be, she put her little instrument to "messenger," sent the current by pulling clown the spring, and in two minutes a messenger was at the door waiting to convey my message to the telegraph-office. Time passes terribly quick, and my energy is gradually disappearing, so that I shall have to pass over some of the things I wanted to show you, such as the process of engraving by the electromagnetic system; how toys were moved, boats made to swim about, and birds to sing. At the recent Paris Exhibition, the varied applications of electricity were simply wonderful and amusing. I have no doubt we shall have a great many of them exhibited, shortly, at the Crystal Palace, where I hope some of you may be able to go before your return to school. I will now show you how this system of producing electro-magnetism can be utilized for telegraphic purposes. On the table are fixed two complete sets of telegraph-instruments, very close to each other, but the set on the right hand belongs to one station, and that on the left hand to another station. You may fancy that the instrument which I touch, on the left, is in London, and that which Mr. Cordeaux touches, on the right, is in Liverpool. For every current of electricity I send from London, I do a little work in Liverpool, and that results in motion, producing sound. The mere depression of my "key" produces electro-magnetism in Liverpool, which attracts a piece of iron and produces a sound. [Illustrated by working the instrument.] The battery attached to my key is in London, and the depression of my key sends on a current which arrives at Liverpool, produces magnetism and sound. By depressing the key rapidly or slowly the sounds may be made correspondingly short or long. [Illustrated.] By an arrangement of dots and dashes, the letters of the alphabet are represented, and experienced clerks can read off the sounds and translate them with astonishing rapidity. To illustrate this to you, I will ask your secretary to write down a short sentence, unknown to my assistants, which shall be sent by one of them, Mr. Cordeaux, on one instrument (supposed to be in Liverpool), and read off by Mr. Cooper on the other instrument (supposed to be in London). [The secretary then handed in a slip of paper to Mr. Preece, and the message it contained was read off by Mr. Cooper, "A merry Christmas to the juveniles."] That is the operation of telegraphy. The sounds are read off as clearly as ordinary spoken language, though mistakes are sometimes made. For instance, a party of young school-girls, out for an excursion once, wished to advise their schoolmistress of their safe arrival at a certain point, and sent the message, "Arrived all right"; but the schoolmistress was horror-stricken to read the message as delivered to her, which read "Arrived all tight." Telegraphically, the difference between the two messages is not great, for the letter R is represented by two dots and a dash, while T is represented by a dash. Another error in transmission was where a message, "Five fathoms and four feet is ample for my wants," was delivered "Five fat sows and four feet"; a cricketing message from Lord's, "Jack, bring up two ground-men," was delivered "Jack bring up £2 10s." And, at the time that Commodore Goodenough was appointed to a station in Australia, the message received was, "A commodore has been appointed good enough for the Australian colonies." The system of telegraphy I have just shown is the ordinary one-way method; but it is possible to send two messages in the opposite direction at the same time upon one wire, and this I can make clear, without going into a detailed explanation, by asking Liverpool to send dashes or long sounds to me while I send dots or rapid sounds to him. [This was done.] We go still further, and send four messages in opposite directions, at the same time upon one wire; that is called quadruples telegraphy. But the acme of telegraphy has been produced in this country by the Wheatstone automatic apparatus. I have a complete set of this apparatus before me. In it the messages are prepared by being punched with little holes (as you now see being done), and I now hold a slip of paper bearing perforations representing the alphabet, which look very much like the patterns used in the Jacquard loom for lace-making. The perforated paper is put in the transmitter, which sends on currents of electricity, representing the holes upon it; these currents of electricity are received by a "receiver," by which they are made to represent dots and dashes recorded on a long slip of green paper, and these dots and dashes indicate to the clerk at the receiving station the message sent. The peculiarity of this instrument is its rapidity, for, by it, instead of being only able to send from thirty to forty words a minute (the limit of the human hand) from 250 to 300 words a minute can be transmitted. At the present moment, there is not a town in this country, where a daily paper is published, that is not in direct communication with London, and receives its intelligence by means of apparatus of this description. Whatever news it is, whether an account of the Canonbury Railway accident, or a panic that may have happened this afternoon in some theatre, or something else now going forward to the country papers, it is being sent by means of this perforated paper and automatic instrument. Those who are interested in the apparatus will be able to examine it closely at the end of the lecture; but it is impossible for me to describe it minutely now, because it would occupy more than one lecture to understand the whole working of the system. It is most extensively employed in this country, where the growth of telegraph business has been enormous. I spoke in somewhat glowing terms of the duties and doings of this automatic apparatus when in Paris, and my Parisian friends rather doubted my statement. However, I induced the French Government to send an officer over to England to examine for themselves the working of this instrument, and to my great pleasure when he came here he found that my statements were under the mark, and only a few days ago, when an experiment was tried, to satisfy the French gentleman, we were able to transmit, on a wire between London and Glasgow, no less than 352 words a minute. The growth of telegraphy in this country has been enormous. In 1869 there were only 2,000 offices open, there are now 5,500; there were then only 0,000,000 messages sent a twelvemonth, there are now 30,000,000; the income in 1809 was £700,000, it is now £1,600,000; the number of newspapers and clubs supplied with news was then only 173, it is now 803; and there are 326 towns now being supplied with news direct from London. In regard to submarine cables, I have here a box of specimens of the various types of cable laid down, which is well worth examination. Submarine telegraphy has increased during the ten years, from a few hundred miles of cable, to 70,000 miles, which now engirdles the world. There are many other applications of electricity besides telegraphy, such as, for instance, railway-signals. A railway accident recently occurred at Canonbury, where three or four trains were huddled up in a tunnel. I do not know much about the system of signaling used on that railway, but I know a good deal of the system of signaling in use on the London and Southwestern Railway and other lines. The principle of the "block" system is simply that a railway is supposed to be divided into certain sections of a given length, and no two trains are allowed, or ought to be allowed, to be in one section at the same time. If, for instance, the section be a tunnel, such as at Canonbury, and two trains are allowed on it, the risk of collision is great, as recently proved; but, if the block system be thoroughly and efficiently carried out, there ought to be no such accidents. Some twenty years ago, after a good deal of talking, writing, and persuading, I induced the London and Southwestern Railway to adopt the block system. The system in use on the London and Southwestern Railway is my own. A complete set of apparatus is before you, and I will explain its working. A little semaphore is in front of the instrument, which, when down, indicates that all is clear, and, when up, that there is danger, and the train must stop. Suppose the instrument near me is at Waterloo Station, and the other one near Mr. Goldstone is at Vauxhall. That represents a section of the railway, upon which we want to allow one train only at a time. To ascertain if all is clear at Vauxhall, I send a warning signal of two beats given twice, indicating "A train is coming," which is acknowledged by a signal of one beat from Vauxhall; my semaphore arm is down, telling me that the line is clear, and I let the train go on, sending a signal of two beats [this was done] to Vauxhall, to tell him that the train is in. Vauxhall raises the semaphore behind the train to prevent me from sending on another, and I acknowledge his signal, by giving one beat of the bell. The train is now proceeding; the semaphore arm at this end is up, protecting the train, and I can not, I dare not, send another train until I know that the one now going on has arrived at Vauxhall. It is now supposed to have done so, and he sends three beats upon the bell, which lowers my semaphore arm and tells me "Line clear," and that the apparatus is in working order. On such a system the traffic of a railway can be conducted day by day, and hour by hour, with safety to the public, and with satisfaction and certainty to the railway interest. One other illustration that I must give you, of the application of electricity, especially as my store of energy is not yet exhausted, is the telephone. One of the most beautiful things at the Paris Exhibition was the transmission of music, by means of the telephone, from the Opera-House to the Exhibition Building. At the Opera-House several microphones were fixed upon the stage, and at the Exhibition Building telephones were fixed in rooms into which visitors could go, and, by applying the telephones to their ears, could listen to the overture of the orchestra, or the singing or talking of the performers, as also the hum of the ballet-girls behind the stage. The effect was something startling. I remember one night seeing a Frenchman put the telephones to his ears, and the moment he heard the sounds he threw down the instruments, and rushed out of the room, saying, "C'est terrible, c'est terrible!" The Christmas holidays have prevented my having similar arrangements for this lecture, and the best thing I could get ready is a telephone circuit between this hall and a neighboring room. I will call up and ask my assistant to play something on a cornet. [The cornet was heard playing quite distinctly.] That is an instance of what I wished to illustrate to you at the commencement; we have a bugler, full of energy, who blows into his bugle, the energy of which takes the form of sound; the sound-waves, or vibrations, strike the top of the telephone-case, and set a microphone in vibration, which causes currents of electricity to pass along the wire from the instrument at the other end to the one before you. In the receiving instrument the currents sent by the microphone take the form of electro-magnetism, and reproduce the vibration of the microphone upon a disk in front of the electro-magnet, and so we get reproduced in the same form the energy set in motion at the other end, after having passed through various stages. The motion of the cornet is transferred, first, into the motion of the disk, then into the electrical form of energy, then into that of electro-magnetism, then back again into motion, and, finally, to your ears; and you will easily understand from this that electric currents are merely one form of energy. I intend to pursue this subject next time, and show you how electricity is produced in other ways, and how it breaks up chemical compounds into their separate parts; how electro-plating and silvering are done; and, finally, I will show how it produces the beautiful Edison electric light we now have in this room. The elegant chandelier now illuminating this room was made especially for exhibition at this lecture, and was prepared by Messrs. B. Verity and Sons, of King Street, Covent Garden.