Alexander Graham Bell

“ I allude to the discovery of radium by Madame Curie of Paris.
Radium has recently upset our most cherished theories of matter and force. The whole subject of chemistry has to be rewritten and our ideas of the constitution of matter entirely changed. Here is a substance which emits light and heat and electricity continuously without any apparent source of supply. It emits light in the dark, and in a cool room maintains itself constantly at a higher temperature than its environment. ”

“ When a telephone is placed in circuit with a telegraph line, the telephone is found seemingly to emit sounds on its own account. The most extraordinary noises are often produced, the causes of which are at present very obscure. One class of sounds is produced by the inductive influence of neighbouring wires and by leakage from them, the signals of the Morse alphabet passing over neighbouring wires being audible in the telephone, and another class can be traced to earth currents upon the wire, a curious modification of this sound revealing the presence of defective joints in the wire. ”

“ Now, pass a rapidly-interrupted beam of light through some substance whose absorption spectrum is to be investigated, and bands of sound and silence are observed upon exploring the spectrum, the silent positions corresponding to the absorption bands. Of course, the ear can not for one moment compete with the eye in the examination of the visible part of the spectrum; but in the invisible part beyond the red, where the eye is useless, the ear is invaluable. In working in this region of the spectrum, lampblack alone may be used in the spectrophonic receiver. ”

“ Dying of thirst in a fog I cannot hope to bring to your attention all of the problems that are awaiting solution, but I think it may be interesting to you to hear of a few upon which I myself have been working. What interests me will probably interest you, and perhaps some of you may carry out the experiments to a further point than I have done.
You know that although I am a lover of Washington, yet, when the summertime comes, I go just as far away from Washington as I can in the direction of the North Pole. ”

“ For several years my attention was almost exclusively directed to the production of an instrument for making and breaking a voltaic circuit with extreme rapidity, to take the place of the transmitting tuning-fork used in Helmholtz’ researches. I will not trouble you with the description of all the various forms of apparatus that were devised, but will merely direct your attention to one of the best of them, shown in fig. 2. In the transmitting instrument T, a steel reed a is employed, which is kept in continuous vibration by the action of an electro-magnet e and local battery. ”

“ Upon consideration of the subject, however, I saw that the experiments could not be conducted in the ordinary way, for the following reason: The law of audibility of the telephone is precisely analogous to the law of electric induction. No effect is produced during the passage of a continuous and steady current. It is only at the moment of change from a stronger to a weaker state, or vice versa, that any audible effect is produced, and the amount of effect is exactly proportional to the amount of variation in the current. ”

“ The reason we cannot keep our houses cool I was once obliged, very much against my will, I can assure you, to remain in Washington right in the midst of the summer, and the thought kept constantly recurring to my mind, If man has the intelligence to heat his house in the winter-time, why does he not cool it in the summer? We go up to the Arctic regions and heat our houses and live. We go down to the Tropics and die. In India the white children have to be sent home to England in order to live, and all on account of the heat. ”

“ It would be premature, without further experiments, to speculate too much concerning the nature of these invisible rays; but it is difficult to believe that they can be heat-rays, as the effect is produced through two sheets of hard rubber, containing between them a saturated solution of alum. Although effects are produced, as above shown, by forms of radiant energy which are invisible, we have named the apparatus for the production and reproduction of sound in this way, the "photophone," because an ordinary beam of light contains the rays which are operative. ”

“ It seemed to me that in this way a number of distinct telegraph messages might be sent simultaneously from the tuning-fork piano to the other end of the circuit, by operators each manipulating a different key of the instrument. These messages would be read by operators stationed at the distant piano, each receiving operator listening for signals of a certain definite pitch, and ignoring all others. In this way could be accomplished the simultaneous transmission of a number of telegraphic messages along a single wire, the number being limited only by the delicacy of the listener’s ear. ”

“ Knowledge is power; and we now realize that the nation that fosters science becomes so powerful that other nations must, if only in self-defense, adopt the same plan. It is safe to say that scientific men and technical experts are destined in the future to occupy distinguished and honorable positions in all the countries of the world. ”

“ We find that when a vibratory beam of light falls upon these substances they emit sounds, the pitch of which depends upon the frequency of the vibratory change in the light. We find, further, that, when we control the form or character of the light-vibration on selenium, and probably on the other substances, we control the quality of the sound and obtain all varieties of articulate speech. We can thus, without a conducting wire, as in electric telephony, speak from station to station, wherever we can project a beam of light. ”

“ We progress from candles to electricity in one lifetime I said it was a glorious thing to be young; but it is also a glorious thing to be old and look back upon the progress of the world during one's own lifetime. ”

“ We can thus understand how it is that a substance like lampblack produces intense sonorous vibrations in the surrounding air, while at the same time it communicates a very feeble vibration to the diaphragm or solid bed upon which it rests.
This curious fact was independently observed in England by Mr. Preece, and it led him to question whether, in our experiments with thin diaphragms, the sound heard was due to the vibration of the disk or (as Professor Hughes had suggested) to the expansion and contraction of the air in contact with the disk confined in the cavity behind the diaphragm. ”

“ An extremely loud musical note is occasioned by the spark of a Ruhmkorff’s coil when the primary circuit is made and broken with sufficient rapidity; when two rheotomes of different pitch are caused simultaneously to open and close the primary circuit a double tone proceeds from the spark.
A curious discovery, which may be of interest to you, has been made by Professor Blake. He constructed a telephone in which a rod of soft iron, about six feet in length, was used instead of a permanent magnet. A friend sang a continuous musical tone into the mouthpiece of a telephone, like that shown in fig. ”

“ Water vapor is given off by the sea everywhere and at all temperatures; it is even evaporated from ice and snow. Of course, the warmer the sea-water is, the greater is the amount of water vapor thrown out; but water vapor is everywhere present, and the main point in condensation is that it is removed from the surface by the action of the wind and carried to cooler places, where condensation occurs in the form of cloud or rain. No great amount of heat is required to produce evaporation and no great amount of cold is necessary to effect condensation. ”

“ For this purpose we have constructed several different forms of apparatus for studying the effects, but, as our researches are not yet complete, I shall confine myself to a simple description of some of the forms of apparatus we have devised.
When a beam of light is brought to a focus by means of a lens, the beam diverging from the focal point becomes weaker as the distance increases in a calculable degree. Hence, if we can determine the distances from the focal point at which two different substances emit sounds of equal intensity, we can calculate their relative sonorous powers. ”

“ Our growing crops and even weeds can be used. The waste products of our farms are available for this purpose and even the garbage from our cities. We need never fear the exhaustion of our present fuel supplies so long as we can produce an annual crop of alcohol to any extent desired.
The world will probably depend upon alcohol more and more as time goes on, and a great field of usefulness is opening up for the engineer who will modify our machinery to enable alcohol to be used as the source of power. ”

“ Without going into details, I shall merely say that the great defects of this plan of multiple telegraphy were found to consist, firstly, in the fact that the receiving operators were required to possess a good musical ear in order to discriminate the signals; and secondly, that the signals could only pass in one direction along the line (so that two wires would be necessary in order to complete communication in both directions) . ”

“ In arranging the apparatus for the purpose of reproducing sound at a distance, any powerful source of light may be used, but we have experimented chiefly with sunlight. For this purpose a large beam is concentrated by means of a lens upon the diaphragm-mirror, and, after reflection, is again rendered parallel by means of another lens. The beam is received at a distant station upon a parabolic reflector, in the focus of which is placed a sensitive selenium-cell, connected in a local circuit with a battery and telephone. ”

“ I had in mind an old lady, who is now living in Baltimore, at the age of one hundred and seven—she is now in her one hundred and eighth year—with mental faculties unimpaired. Possessed of a bright and active mind, she is able, from her own personal recollections, to look back upon a whole century of progress of the world. ”

“ In laboratory experiments the transmitting and receiving instruments are necessarily within ear-shot of one another, and we have, therefore, been accustomed to prolong the electric circuit connected with the selenium receiver, so as to place the telephones in another room. By such experiments we have found that articulate speech can be reproduced by the oxyhydrogen light, and even by the light of a kerosene-lamp. The loudest effects obtained from light are produced by rapidly interrupting the beam by the perforated disk. ”

“ When I was a young man the institutions of learning, the higher schools and colleges, paid a great deal more attention to the teaching of Latin and Greek than to the study of science; they made scholars rather than scientists. ”

“ We found the effect intensified by arranging the sheet of hard rubber as a diaphragm, and listening though a hearing-tube. We then tried crystalline selenium in the form of a thin disk, and obtained a similar but less intense effect. The other substances which I enumerated at the beginning of my address were now successively tried in the form of thin disks, and sounds were obtained from all but carbon and thin glass. We found hard rubber to produce a louder sound than any other substance we tried, excepting antimony, and paper and mica to produce the weakest sounds. ”

“ One of the great evils attending our civilization is the extreme congestion of the population into the larger cities, and one of the great problems of the future is how to spread the population more equally over the land.
The congestion is caused by difficulties of transportation; for, of course, it costs much more to send a person to a distant place than to one near at hand. ”

“ We have observed that melted selenium behaves to the other substances as water to a greasy surface, and we are inclined to think that, when selenium is used in connection with metals not chemically acted upon by it, the points of contact between selenium and the metal offer a considerable amount of resistance to the passage of a galvanic current. By using brass we have been enabled to construct a large number of selenium-cells of different forms. The mode of applying the selenium is as follows: The cell is heated, and, when hot enough, a stick of selenium is rubbed over the surface. ”

“ All that is necessary is a current of air over your salt water to remove the water vapor collected there, and then the carrying of this confined current into a cool reservoir where the water may condense.
The thermos-bottle idea applied to a water tank As little or no artificial heating is required, a great saving can be effected in the matter of fuel. It is extraordinary how wasteful we are in our means of producing heat and in retaining it after it has been produced. It is safe to say that a great deal more heat goes up the chimney than we utilize from a fire. ”

“ In science every failure advances the boundary of knowledge as well as every success, and Berzelius felt that, if the characteristic odor that had been observed did not proceed from tellurium, it might possibly indicate the presence of some substance then unknown to the chemist. ”

“ At a central station steam-engines pump air into the pipes and keep up a continuous pressure of from four to five atmospheres. As there are several hundred kilometers of these pipes under the streets of Paris, they form a huge reservoir of compressed air at the ground temperature.
In the cooling room of a café they simply turn a little cock and admit the compressed air into the room. A gas meter measures the amount of air admitted and charges are made accordingly. ”